Isothermal and anisothermal creep behavior of the nickel base Alloy 602 CA

Components in industrial furnaces and apparatus construction are usually exposed to temperatures up to 1,200 °C as well as mechanical loading and corrosive attack of the environmental atmosphere. Furthermore, they undergo numerous temperature cycles in service. To describe the characteristics of the nickel base Alloy 602 CA, which is often used in this industrial sector, the long term creep behavior of this alloy was studied at temperatures from 800 °C to 1,200 °C with and without thermal cycling. During these tests unexpected effects could be noticed. At load levels representing typical component loads and isothermal temperature control an anomalous decrease in creep rate in the third creep stage was observed. Experiments under thermal cycling showed a considerably higher creep rate in the whole range than in the isothermal case. Within the present article, these findings are outlined in detail together with a brief discussion of causes and consequences based on extensive microstructural examinations.     

Zur thermischen Ermüdung der Magnesium‐Basislegierung AZ91

Thermal fatigue of magnesium‐base alloy AZ91 Thermal fatigue tests of the magnesium‐base alloy AZ91 were carried out under total strain control and out‐of‐phase‐loading conditions in a temperature range between ‐50°C and +190°C. Specimens produced by a vacuum die casting process were loaded under constant total strain and uniaxial homogeneous stress. To simulate the influence of different mean stresses, experiments were started at different temperature levels, e.g. the lower, mean or upper temperature of the thermal cycle. The thermal fatigue behavior is described by the resulting stress amplitudes, plastic strain amplitudes and mean stresses as a function of the number of thermal loading cycles. Depending on the maximum temperature and the number of loading cycles, cyclic softening as well as cyclic hardening behavior is observed. Due to the complex interaction of deformation, recovery and recrystallization processes and as a consequence of the individual temperature and deformation history, thermal fatigue processes of the material investigated cannot be assessed using results of isothermal experiments alone. The upper temperatures or the resp. temperature amplitudes determine the total fatigue lifetime.     

Isothermal and thermomechanical fatigue behaviour of a high temperature titanium alloy

Abstract

Isothermal and thermomechanical fatigue (TMF) behaviour (including cyclic stress response and number of cycles to failure) of a Ti – 5.6Al – 4.8Sn – 2.0Zr – 1.0Mo – 0.32Si – 0.8Nd (wt-%) hightemperature titanium alloy was examined. The purpose of the present investigation was to understand the effect of temperature fluctuation on the cyclic behaviour and fatigue life of this alloy and to test the suitability of lifetime prediction based on isothermal laboratory data. The results indicated that both the level of peak stress and fatigue life were decreasing with increasing test temperature from 400°C to 650°C in isothermal fatigue (IF) tests. In TMF tests run between 400°C and 600°C, the peak stresses corresponding to 600°C coincide well with that found in IF tests run at 600°C, while a slight increase in cyclic hardening was found for peak stress corresponding to 400°C compared to that found in a 400°C/IF test. This increase in cyclic hardening became more pronounced when the maximum temperature increased to 650°C. Fatigue life in 'out of phase' (OP) condition was found to be shorter than under an equivalent 'in phase' (IP) condition, and this gap increased with decreasing mechanical strain amplitude. The results indicate that lifetime prediction based on isothermal laboratory data may lead to non-conservative results if thermal fluctuations are present in components made of the present alloy.     

Stress Evolution With Temperature in Titanium‐Rich NiTi Shape Memory Alloy Films

Abstract: The effect of deposition temperature on residual stress evolution with temperature in Ti‐rich NiTi films deposited on silicon substrates was studied. Ti‐rich NiTi films were deposited on 3″ Si (100) substrates by DC magnetron sputtering at three deposition temperatures (300, 350 and 400 °C) with subsequent annealing in vacuum at their respective deposition temperatures for 4 h. The initial value of residual stress was found to be the highest for the film deposited and annealed at 400 °C and the lowest for the film deposited and annealed at 300 °C. All the three films were found to be amorphous in the as‐deposited and annealed conditions. The nature of the stress response with temperature on heating in the first cycle (room temperature to 450 °C) was similar for all three films although the spike in tensile stress, which occurs at ～330 °C, was significantly higher in the film deposited and annealed at 300 °C. All the films were also found to undergo partial crystallisation on heating up to 450 °C and this resulted in decrease in the stress values around 55–60 °C in the cooling cycle. The stress response with temperature in the second thermal cycle (room temperature to 450 °C and back), which is reflective of the intrinsic film behaviour, was found to be similar in all cases and the elastic modulus determined from the stress response was also more or less identical. The three deposition temperatures were also not found to have a significant effect on the transformation characteristics of these films such as transformation start and finish temperatures, recovery stress and hysteresis.     

Effect of heating temperature and magnesium content on the thermal cyclic failure behaviour of ductile irons

Abstract

This study elucidates the effect of residual magnesium content and heating temperature on the thermal cyclic failure behaviour of ductile irons by applying repeated heating and cooling cycles. Five irons with different residual magnesium contents ranging from 0.038 to 0.066 wt-% were obtained by controlling the amount of nodulariser additions. The thermal fatigue cracking behaviour was investigated during thermal cycling from 25°C to 650, 700, 750, and 800°C, respectively. Experimental results indicate that the thermal fatigue cracking resistance of ductile iron decreases with increasing residual magnesium content. The maximum heating temperatures of 700°C and 750°C led to the most severe thermal fatigue cracking in the specimens containing 0.054 wt-% and 0.060 wt-% residual magnesium content. Recrystallisation of ferrite grain occurred when the thermal cycles exceeded a certain number after testing at 800°C, which deferred the initiation of thermal fatigue cracking.     

Thermoschockbeständigkeit und das Verhalten von SiC-faserverstärkten Glas-Matrix-Verbundwerkstoffen bei einer thermischen Wechselbeanspruchung

The damage evolution of commercially available SiC-Nicalon? fiber-reinforced glass matrix composites under thermal shock and thermal cycling conditions in oxidizing atmospheres was investigated. The thermal shock tests involved quenching the samples from high temperatures (590–710°C) to room temperature in a water bath. For the thermal cycling tests the samples were quickly alternated between high temperature (T=700°C) and room temperature air for different number of cycles. Both destructive and non-destructive techniques were employed to characterize the samples and to detect differences in behavior for the various thermal loading conditions. In thermally shocked samples, damage in the form of matrix microcracks was induced by quenching from intermediate temperatures, e.g. 660°C. The extent of damage increased with the number of thermal shock cycles, as detected by a decrease in the Young’s modulus and a simultaneous increase in the internal friction measured non-destructively be a mechanical force resonance technique. In thermally cycled samples, material degradation was ascribed to porosity formation in the matrix as a consequence of the extended exposures at high temperatures. With increasing number of cycles, also interfacial oxidation was detected. An attempt was made also to explore the possibility of healing the induced microcracks in thermally shocked samples by an optimized post-thermal shock heat-treatment (annealing) schedule, exploiting the viscous flow of the glass matrix.     

Zwillingsbildung bei der thermischen Ermüdung der Mg‐Basislegierung AZ31

Twinning at thermal fatigue of magnesium alloy AZ31 In this paper results of thermal fatigue tests of the magnesium base alloy AZ31 carried out in a temperature range between ‐50 °C and +290 °C are presented. Specimens were loaded under constant total strain and uniaxial homogeneous stresses. The resulting materials behaviour is described by stress amplitudes, plastic strain amplitudes and mean stresses as a function of the number of thermal loading cycles. It is well known that AZ31 shows different stress‐strain behaviour during tensile and compressive loading resp. at lower temperatures due to the fact that mechanical twinning depends on the loading direction. However untwinning processes may occur during unloading and reloading in the opposite direction. As a consequence, during the first thermal loading cycles, typical consequences of the formation and the dissolution of twins are observed. The interaction of deformation, recovery and recrystallization processes, characteristic for individual temperature ranges are discussed in detail to analyze the damage progress during thermal fatigue.     

Modeling of creep and stress relaxation of the nickel‐base alloy NiCr20TiAl at isothermal and non‐isothermal loading conditions

The design and dimensioning of new as well as the assessment of operating high‐temperature components in service require a precise prediction of creep and stress relaxation. The increasing share of renewable energies forces fossil‐fired power plants for increasing numbers of start‐ups and shut‐downs. Consequently, transient loading conditions need to be taken into account. In order to meet this demand, non‐isothermal creep equations are necessary, which enables a consistent prediction of creep strain and stress relaxation in a wide range of temperatures and stresses. In this paper, an approach for the visco‐plastic modeling of creep and stress relaxation for non‐isothermal loading conditions is presented. The strain portions creep, “negative creep” and initial plasticity, occurring at elevated temperatures are described by temperature‐dependent phenomenological equations. Within this paper, the adjustment of the parameters is based on a wide database of hot tensile tests, creep and annealing experiments. The nickel‐base alloy NiCr20TiAl has been examined in a temperature range from 450 °C to 650 °C. The developed material models have been successfully validated with isothermal and non‐isothermal relaxation experiments. Further, the recalculation of a staged relaxation test demonstrates the capability of the defined material laws in a wide stress range under isothermal and non‐isothermal loading conditions.     

Phase transitions in coated nickel titanium arch wires: A differential scanning calorimetric and X-ray diffraction analysis

Shape memory and super-elastic properties of orthodontic nickel titanium wires, which are crucial for its clinical performance are dependent on the austenitic–martensitic phase transitions in its metallic microstructure that happen as a result of temperature or stress. The objective of this study was to compare the austenitic–martensitic phase transitions in new, black oxide coated nickel titanium (0·016 inch, Black Diamond, NiTi) arch wires in the ‘as-received’ form, from the manufacturer and ‘retrieved form’ after two months of intraoral use. This was done to analyse whether the new oxide coated nickel titanium wires suffered any significant loss in shape memory and super elasticity properties at the end of two months of intra oral use, findings of which could give valuable inferences prior to its widespread application in clinical practice. Five arch wire samples in both groups were investigated for their austenitic–martensitic phase transitions in an in vitro set up, using differential scanning calorimetry (DSC), (?90° to 100°C at a rate of 10°C/min) and X-ray diffraction (XRD) analysis (10° to 90°), as a function of temperature. Martensitic–austenitic thermograms showed an intermediate rhombohedral phase in the heating cycle of both groups, but cooling cycles showed direct reversal from austenitic to martensitic phase. Lower austenitic start ( $A_{\rm \textbf{s}}$ = 10·78 ± 0·46°C) and finish ( $ {A}_{\rm \textbf{f}}$ = 22·26 ± 0·24°C) temperatures of coated wires compared to the conventional wires showed (i) ability of the wire to remain in austenitic phase below oral temperature, that permits it to take up greater force during activation, (ii) increased springiness and (iii) consistent force delivery for an extended period of time. Statistical analysis with paired Student’s ‘t’ test did not show any significant difference in mean values of transition temperatures and enthalpies between the two groups which proved similar shape memory and super-elastic properties at the end of intra oral use. Black oxide coating of NiTi wires may, therefore, be effective in diversified oral conditions and may find acceptable for re-use after sterilization. Low enthalpy values (0·92–3·59 j/g) compared to conventional ones, implied complete phase transition at the atomic level that can improve performance of the material in activation and deactivation cycles of NiTi wires. X-ray diffraction analysis of the two groups demonstrated predominance of austenitic phases (A, 110, 220 and 211) with complete reversibility at the atomic level. Discrete crystallographic structure and absence of multiple phases showed complete martensitic–austenitic transition, which authenticated the differential scanning calorimetric findings. This can earn acceptance for the new product in contemporary orthodontic practice with adequate scope for indigenization.     

Enhancing modulus and ductility of Mg/SiC composite through judicious selection of extrusion temperature and heat treatment

Abstract

In the present study, a magnesium based composite with about 11.5 wt-%SiC particulates was synthesised using an innovative disintegrated melt deposition technique followed by extrusion at different temperatures of 350°C, 250°C, 150°C and 100°C. Microstructural characterisation of the extruded samples showed an increase in alignment of SiC particulates in the direction of extrusion, reduction in number of SiC particulate clusters and improved distribution of the SiC particulates as the extrusion temperature decreased. Good interfacial integrity and minimal porosity was also observed for all the samples. Mechanical properties characterisation revealed that a decrease in extrusion temperature from 350°C to 100°C led to a significant increase in hardness, elastic modulus, 0.2% yield strength while the average UTS and ductility remain unaffected. Subsequently, isothermal heat treatment at 100°C with holding times of 5 and 10 h were also carried out for samples that were extruded at 100°C. The results of tensile testing revealed that the heat treatment led to an approximately 3.6 times increase in ductility, did not affect the modulus. Considering the standard deviation, the 0.2% yield strength and UTS remained similar. An attempt is made in the present study to correlate the effect of decreasing the extrusion temperature as well as subsequent heat treatment with the microstructural and mechanical behaviour of the composite.     

Technologische Eigenschaften warmgewalzter Bleche großer Formate aus Titan für den Anlagenbau

Mechanical Properties of Hot Rolled Plates of Large Size for Plant Engineering Large size plates of commercially pure titanium grade 1, 2 and 3 according to DIN 3.7025, 3.7035 and 3.7055 up to 3500 mm width and a maximum length of 10000 mm with a thickness of 7 and 30 mm have been tested. They fullfill the acceptance specifications for hot rolled plates of conventional size regarding flatness, thickness tolerances and mechanical properties at room temperature. The availability of plates with a very high flatness creates the basis for large sizes explosion cladding with commercially pure titanium as surface layer material. Additional investigations between ? 196°C and + 400°C for the mechanical properties and notched impact strength of plates and weldments as well as fatigue strength at room temperature show, independent of the rolling direction, the possible influence of grain size and interstitials like oxygen and hydrogen as well as of the iron content on the properties. The notched impact strength has a maximum at 100°C without a steep drope at lower temperatures. The decrease of tensile strength and proof stress with increasing temperature show a retarding effect at 150°C. The elongation reaches a maximum at 200°C, combined with a low ratio of yield strength to tensile strength.     

High-temperature fatigue behaviour of a second generation near-γ titanium aluminide sheet material under isothermal and thermomechanical conditions

The high-temperature deformation behaviour of a second generation γ-TiAl sheet material with near-γ microstructure was characterised under tensile, creep, isothermal and thermomechanical fatigue (TMF) loading conditions. Test temperature ranged from 500 to 750 °C in isothermal tests and these temperatures were also used as minimum and maximum temperature of in-phase (IP) and out-of-phase (OP) thermomechanical fatigue tests. Under tensile loading, a ductile-to-brittle transition temperature (DBTT) of about 650 °C was observed. At this temperature the material experiences a temperature dependent change in the fracture morphology. Creep tests carried out in the temperature range from 650 to 800 °C under true constant stress conditions revealed a temperature and stress dependence of the Norton stress exponent n and the apparent activation energy for creep Q_app. With increasing temperature, isothermal fatigue life at constant strain amplitude decreased in vacuum, but increased in air indicating an abnormal (inverse) environmental effect. Under IP loading, fatigue is characterised by cyclic softening due to dynamic recrystallisation. OP loading drastically reduces fatigue life and turned out to be an extremely critical loading situation for γ-TiAl alloys.     

Durability of cementitious binder derived from industrial wastes

The durability of cementitious binder hydrated at 27°C and 50°C under high humidity was examined by alternate wetting and drying, as well as heating and cooling, cycles at temperatures ranging from 27°C to 60°C and by performance in water. The results show that cementitious binder hardened at 50°C possesses higher water resistance and lower porosity than the binder hardened at 27°C. A decrease in the strength of the cementitious binder was observed with an increase in temperature and in the wetting and drying and heating and cooling cycles. The maximum decrease in strength occurred at 60°C. The cementitious binder cured at 27°C showed a much smaller decrease in strength with a rise in temperature and in weathering cycles. The changes in strength of the cementitious binder were monitored by differential thermal analysis and microscopy.     

Chemical and thermomechanical tailoring of the shape memory effect in poly(ε-caprolactone)-based systems

The thermally activated shape memory response of polymeric materials results from a combination of the material molecular architecture with the thermal/deformational history, or ‘programming’. In this work, we investigate the shape memory response of systems based on poly(ε-caprolactone) (PCL) so as to explore the adoption of proper chemical and thermomechanical tailoring routes. Cross-linked semicrystalline PCL-based materials are prepared by different molecular architectures starting from linear, three- and four-arms star PCL functionalized with methacrylate end groups, allowing to tune the melting temperature, T _m, ranging between 36 and 55 °C. The materials’ ability to display the shape memory is investigated by the application of proper thermomechanical cycles on specimens deformed at two different temperatures (23 and 65 °C, i.e. below and above the T _m, respectively). The shape memory response is studied under dynamic thermal conditions in thermally activated recovery tests, to identify the typical transformation temperatures, and under isothermal conditions at given recovery temperatures, to monitor shape recovery as a function of time. All the specimens are capable of full recovery on specific thermal ranges influenced by both melting and deformation temperatures. Specimens deformed above T _m are able to recover the whole deformation in a very narrow temperature region close to T _m, while those deformed at room temperature display broader recovery processes, those onset at about 30 °C. Isothermal tests reveal that when the deformed material is subjected to a constant recovery temperature, the amount of recovered strain and the time required strongly depend on the particular combination of melting temperature, deformation temperature and recovery temperature.     

Effects of annealing process on microstructure and electrical properties of cold-drawn thin layer copper cladding steel wire

The microstructure, mechanical and electrical properties of cold-drawn thin layer copper cladding steel (CCS) wires annealed after different processes were studied by optical microscopy, electron omnipotent material experiment machine, micro hardness machine, SEM and electrical resistivity measurement system. The results indicated that the recovery and recrystallization of steel-core happened in the temperature range 550–750 °C for the holding period of 120 min. When the annealing temperature was higher than 750 °C, grains begun to grow and grain sizes increased gradually with increasing the annealing temperature. The tensile strength and micro hardness were declined with increasing annealing temperature and holding time. The distance of Cu–Fe atoms interfacial diffusion of thin layer CCS wires ranged from 4 µm of cold-drawn wire to 7.5 µm of annealed wire at 850 °C for 120 min. The higher the annealing temperature become, the larger the distance of Cu–Fe atoms interfacial diffusion is. When the annealing temperature was lower than 650 °C, the resistivity was slightly less than 71 × 10^?3 Ω mm² m^?1 which was the resistivity of cold-drawn wire. When the annealing temperature was higher than 650 °C, the resistivity increased with increasing the annealing temperature. Meanwhile, the variation of electrical property of thin layer CCS wires was analyzed and discussed based on microstructure and interfacial diffusion.     

Effect of process parameters on semi-solid TLP bonding of Ti–6Al–4V to Mg–AZ31

The semi-solid transient liquid-phase bonding (Semi-solid TLP bonding) of titanium alloy Ti–6Al–4V to magnesium alloy Mg–AZ31 was performed using a eutectic forming nickel foil. The process parameters were optimized to achieve higher shear strength. The effect of temperature and pressure on microstructure evolution and mechanical characteristics were examined for bonding time between 5 and 60 min. Three reaction layers L1, L2 at Ni/Mg–AZ31 interface and L3 along the Ni/Ti–6Al–4V interface were determined within joint zone at a bonding temperature of 515 °C. The L1 and L2 reaction layers continued to be seen when the bonding temperature increased to 540 °C. When the bonding pressure increases from 0.2 to 0.7 MPa, a new reaction layer L4, at the Ni/Ti–6Al–4V interface was observed. The results showed that as the bonding time increased up to 60 min, the width of the joint decreased due to isothermal solidification. Maximum shear strength of 39 MPa was obtained for 540 °C and 0.2 MPa with a holding time of 20 min. However, further increase in bonding time to 60 min resulted in a decrease in shear strength to 8 MPa, and this decrease in strength was attributed to the increase in intermetallics forming within the joint zone.     

Low temperature annealing behavior of electroplated nickel

The low temperature annealing characteristics of electroplated nickel containing an occluded brightener, fuchsin, have been studied in the temperature range 25–250°C. Supportive annealing experiments were also conducted between the temperatures 250°C and 700°C to assist in evaluating the lower temperature behavior. The effect of annealing was monitored by measuring resistivity changes at liquid nitrogen temperatures and by viewing selected samples by transmission electron microscopy. In addition, various chemical analysis techniques were employed to follow the variations in impurity content.A detailed comparison was made between deposits from a standard “watts” nickel electrolyte and those from a “watts” nickel solution containing the fuchsin additive. Isochronal anneals of fuchsin-containing deposits were characterized by a large decrease in resistivity up to a temperature of 175°C. Higher temperature annealing from 175°C to 275°C demonstrated an increase in resistivity with increasing temperature. This increase was then followed by a general decrease in resistivity at temperatures greater than 350°C. The first two minima at 175°C and 300°C on the Δ?°/Δ? versus temperature curve were found to coincide with temperatures where partial decomposition of the fuchsin reagent occured.The low temperature resistivity decrease from 28°C to 125°C was attributed to the diffusion of divacancies to fixed sinks such as grain boundaries. A high non-equilibrium vacancy concentration is believed to be present owing to the accommodation of fuchsin molecules in the nickel lattice. The resistivity decay is described by an Arrhenius-type equation:

$\text{dp}\text{dt}\text{=K exp}\text{?}\text{19.4 kcal}\text{RT}$

The experimentally determined activation energy agrees favorably with literature values for divacancy diffusion in nickel. During this interval no visual change in structure was noted, and fuchsin could be extracted from the deposit unaltered.     

Thermal cycling and isothermal oxidation behavior of quadruple EB‐PVD thermal barrier coatings

Increase of energy efficiency by increasing the turbine inlet temperature is the main driving force for further investigations regarding new thermal barrier coating materials. Today, thermal barrier coatings consisting of yttria stabilized zirconia are state of the art. In this study, thermal barrier coatings consisting of 7 weight percent yttria stabilized zirconia (7YSZ) and pyrochlore lanthanum zirconate (La₂Zr₂O₇) were deposited by electron beam physical vapor deposition. Regarding thermal cycling and isothermal oxidation behavior different layer architectures such as mono‐, double‐ and quadruple ceramic layers were investigated. The thermal shock behavior was examined by thermocycle tests at temperatures in the range between T = 50 °C ‐1,150 °C. Additionally, the isothermal oxidation behavior at a temperature of T = 1,150 °C with dwell times of t= 50 h and t = 100 h was studied in the present work. The conducted research concerning the behavior of various thermal barrier coating systems under thermal cycle and isothermal load highlights the potential of multilayer thermal barrier coatings for operating in high temperature areas.     

Experience with the use of the acoustic emission technique for monitoring scale failure in wet and dry environments

Abstract

A brief survey of the acoustic emission technique for monitoring scale cracking and failure on 2.25–24% Cr steels in wet and dry environments is given. A number of acoustic emission test rigs are described. Some of the more simple test rigs are used for testing small oxidation coupons during isothermal oxidation. More sophisticated rigs have been used for testing full size heat exchanger tubes during thermal cycling.

Most acoustic emission measurements in a wet environment come from testing at temperatures below 650°C. There are examples from Alloy 800 and thermal barrier coatings that were tested at higher temperatures, 900°C and 1100°C, respectively. Through the years acoustic emission tests have been performed in dry air, dry air+10%H₂O, dry air+0.5%SO₂, and Ar+5%H₂+50%H₂O. Consequently, a wide variety of exposure temperatures and atmospheres can be investigated using acoustic emission techniques.

Qualitative acoustic emission results can detect when scale cracking occurs at exposure temperature, where such cracks are produced by growth stress. Acoustic emission signals have been measured during sample cooling, where the signal arises from scale cracking that is caused by the thermal expansion mismatch stress. Measured results have clearly shown that scale cracking caused by both growth stress and thermal expansion mismatch stress are affected by water vapor in the exposure environment. Post-test metallographic investigations show that crack orientation and the oxide scale phases are also affected by the gas composition in the test rig. Additionally the sample mass gain and scale thickness is affected by water vapor content.

Finally, acoustic emission techniques are helpful for understanding the phenomena of breakaway oxidation and spallation/exfoliation.     

Residence Time Distribution of Segregating Sand Particles in a Rotary Drum

Leaching, which is described as the extraction of soluble constituents from a solid by means of a solvent, is an important separation technique in the refining of precious metals from their matte. It is, therefore, important to investigate the extraction behavior of metals from the matte, which is the focus of this study. This study reports the influence of concentration of the solvent (ammonia), leaching temperature, leaching time, and pH on the recovery of nickel and copper from the matte. The elemental composition analysis of the matte indicated that it contains 23% copper, 37% nickel and 1.1% ferrous compound. The analysis also showed that the major mineral phases present in the matte were heazlewoodite (Ni₃S₂), chalcocite (Cu₂S), djurleite (Cu1.9S), and nickel alloy. The leaching parameters studied were concentration of ammonia (1.5, 2.0, 2.5, and 3.0 M), leaching time (0–270 min, at 15 min sampling interval), leaching temperatures (50°C, 60°C, and 70°C), and pH (9.3–11.2). The results obtained revealed that the recovery of nickel and copper from the matte was greatly influenced by the concentration of ammonia, leaching time, leaching temperature, and pH. It was established from this study that the highest dissolution of nickel and copper was obtained at 3 M and 2 M ammonia concentration, respectively. The results also revealed that a decrease in the pH of the solution resulted in a decrease in both nickel and copper recovery, with maximum leaching time of 270 min. It was observed that less than 50% of both nickel and copper was leachable due to the presence of metal alloys. The analyses of the results also showed that as the leaching temperature increased from 50°C to 60°C, the amount of nickel and copper that was recovered from the matte significantly increased. However, there was reduction in the amount of nickel and copper recovered from the matte as the temperature was increased from 60°C to 70°C, due to loss of ammonia by evaporation. The shrinking core model was used to explain the behavior of the recovery of these metals at different temperatures, and both metals were found to be favored by diffusion controlled reaction.