High temperature deformation behavior of a near alpha Ti600 titanium alloy

The high temperature deformation behavior of a near alpha Ti600 titanium alloy was investigated with isothermal compression tests at temperatures ranging from 800 to 1000 °C and strain rates ranging from 0.001 to 10.0 s⁻¹. The apparent activation energy of deformation was calculated to be 620.0 kJ mol⁻¹, and constitutive equation that described the flow stress as a function of the strain rate and deformation temperature was proposed for high temperature deformation of Ti600 titanium alloy in the α + β phase region. The processing map was calculated to evaluate the efficiency of the forging process in the temperatures and strain rates investigated and to recognize the instability regimes. High efficiency values of power dissipation over 55% obtained under the conditions of strain rate lower than 0.01 s⁻¹ and temperature about 920 °C was identified to represent superplastic deformation in this region. Plasticity instability was expected in the regime of strain rate higher than 1 s⁻¹ and the entire temperature range investigated.     

Hot deformation behavior and microstructure evolution of twin-roll-cast Mg–2.9Al–0.9Zn alloy: A study with processing map

The hot deformation behavior and microstructure evolution of twin-roll-cast of Mg–2.9Al–0.9Zn–0.4Mn (AZ31) alloy has been studied using the processing map. The tensile tests were conducted in the temperature range of 150–400 °C and the strain rate range of 0.0004–4 s⁻¹ to establish the processing map. The different efficiency domains and flow instability region corresponding to various microstructural characteristics have been identified as follows: (i) the continuous dynamic recrystallization (CDRX) domain in the range of 200–280 °C/≤0.004 s⁻¹ with fine grains which provides a potential for warm deformation such as deep drawing; (ii) the discontinuous dynamic recrystallization (DDRX) domain around 400 °C at high strain rate (0.4 s⁻¹ and above) with excellent elongation which can be utilized for forging, extrusion and rolling; (iii) the grain boundary sliding (GBS) domain at slow strain rate (below 0.004 s⁻¹) above 350 °C appears abundant of cavities, which result in fracture and reduce the ductility of the adopted material; and (iv) the flow instability region which locates at the upper left of the processing map shows the metallographic feature of flow localization.     

Effects of strain on the workability of a high strength low alloy steel in hot compression

Based on the experimental results from the hot compression tests of 42CrMo steel, the efficiencies of power dissipation and instability parameter were evaluated. The effects of strain on the efficiency of power dissipation and instability parameter of 42CrMo steel have been discussed in detail. Processing maps were constructed by superimposition of the instability map over the power dissipation map. The dynamic recrystallization domains and instable zones were identified in the processing map. The effects of strain on microstructural evolutions were correlated with the processing maps. According to the 3D processing maps, the optimum domain of hot deformation is in the temperature range of 1050–1150 °C and strain rate range of 0.01–3 s⁻¹, with its peak efficiency of 32% at about 1140 °C and 0.23 s⁻¹, which are the optimum hot working parameters.     

The tensile deformation behavior of Ti–3Al–4.5V–5Mo titanium alloy

The tensile deformation behavior of Ti–3Al–4.5V–5Mo titanium alloy was studied. The results show that there are obvious yield points on true stress–true strain curves of annealing structures, then a stress drop occurs. The curves show linear work-softening after yielding at annealing temperature of 720–780 °C and linear work-hardening at annealing temperature of 800–840 °C. Elastic energy stored in the α-phase is dramatically released after plastic deformation of the β-phase, which leads to the stress drop.     

Plastic deformation behavior in dual-phase Ni–31Al intermetallics at elevated temperature

Plastic deformation behavior of dual-phase Ni–31Al intermetallics at elevated temperature was examined. It was found that the alloy exhibited good plasticity under an initial strain rate of 1.25 × 10⁻⁴ s⁻¹ to 8 × 10⁻³ s⁻¹ in a temperature range of 950–1075 °C. A maximum elongation of 281.3% was obtained under an initial strain rate of 5 × 10⁻⁴ s⁻¹ at 1000 °C. The strain rate sensitivity, m value was correlated with temperature and initial strain rate, being in the range of 0.241–0.346. During plastic deformation, both the two phases Ni₃Al and NiAl in dual-phase Ni–31Al could co-deform without any void formation or debonding, the initial coarse microstructure became much finer after plastic deformation. Dislocation played an important role during the plastic deformation in dual-phase Ni–31Al alloy, the deformation mechanism in dual-phase Ni–31Al could be explained by continuous dynamic recovery and recrystallization.     

The influence of dynamic strain aging on the low cycle fatigue behavior of near alpha titanium alloy IMI 834

Total strain controlled low cycle fatigue tests on IMI 834 have been conducted in air in the temperature range between 375 and 500 °C at a temperature interval of 25 °C at the nominal strain rate of 6.67 × 10⁻⁴ s⁻¹. The observed maximum peak stress ratio, minimum half-life plastic strain range and lower fatigue life at 425 °C indicates the occurrence of dynamic strain aging (DSA). Pronounced deformation bands, increased dislocation density and non-uniform dispersion of dislocations inside primary α grains observed by the study of transmission electron microscopy supports the occurrence of dynamic strain aging. Initial cyclic softening was attributed to shearing of Ti₃Al precipitates as revealed by TEM evidences.     

ZnO sputter coating on SnO2 nanowires: Effects of thin coating and subsequent thermal annealing

The structural and optical properties of SnO₂–ZnO core–shell nanowires were studied and the effects of thermal annealing were investigated. As-prepared SnO₂–ZnO core–shell nanowires exhibited a smooth and continuous shell layer along the nanowire, with a thickness in the range of 5–10 nm. While the thin ZnO shell layer disappeared after annealing at 800 °C, this did not occur after annealing at 600 °C. The as-fabricated SnO₂–ZnO core–shell nanowires exhibited yellow emission, presumably from the core SnO₂ nanowires. The UV emission from ZnO shell layer was obtained by annealing at 600 °C, whereas it was removed by annealing at 800 °C.     

Hot deformation characteristics of 2205 duplex stainless steel based on the behavior of constituent phases

High temperature behavior of 2205 duplex stainless steel was studied by considering behavior of each constituent phase. The specimens were subjected to hot compression tests at temperatures of 800–1100 °C and strain rates ranging from 0.001 to 1 s⁻¹ at intervals of an order of magnitude. The flow stress analysis showed that hot working empirical constants are different at low and high temperatures. The strain rate sensitivity m was determined and found to change from 0.12 to 0.21 for a temperature rise from 800 °C to 1100 °C. The apparent activation energy Q was calculated as 554 and 310 kJ/mol for low and high temperature, respectively. The validity of constitutive equation of hyperbolic sine function was studied and stress exponent, n, was assessed to be 4.2. Assuming the hyperbolic sine function for determination of strain rate and application of the rule of mixture, the interaction coefficients of δ-ferrite, P, and austenite, R, were estimated at different hot working regimes. It was found that the interaction coefficients are functions of Zener–Hollomon parameter Z and obey the formulas P = 1.4Z^−0.08 and R = 0.76Z^0.005. Therefore, it was concluded that at low Z values δ-ferrite almost accommodates strain and dynamic recovery is the prominent restoration process which may even inhibit dynamic recrystallization in austenite. Otherwise, at high Z, austenite controls the deformation mechanism of material and dynamic recrystallization leads in finer microstructure.     

Growth and mechanical properties of GeSi bulk crystals

Bulk crystals of Ge_1–xSi _x alloys were grown by the Czochralski technique. Full single crystals were obtained for the alloys of composition 0 < x < 0.15 and 0.9 < x < 1, while single crystal parts near the seeds of ingots provided alloys of intermediate composition. The dislocation velocity and mechanical strength of the GeSi alloys were investigated by the etch pit technique and compressive deformation tests, respectively. In the GeSi alloys of the composition range 0.004 < x < 0.080 the dislocation velocity decreases monotonically with increasing Si content in the temperature range 450–700°C and the stress range 3–24 MPa. In contrast, in the composition range 0.94 < x < 1 the dislocation velocity first increases and then decreases with decreasing Si content in the temperature range 750–850°C and the stress range 3–30 MPa. The velocity of dislocations was determined as functions of stress and temperature. The stress–strain behaviour in the yield region of the GeSi alloys of composition 0 < x < 0.4 is similar to that of Ge at temperatures lower than about 600°C. However, the yield stress becomes temperature-insensitive at high temperatures and increases with increasing Si content. The stress–strain curves of the GeSi alloys of composition 0.94 < x < 1 are similar to those of pure Si at temperatures of 800–1000°C and the yield stress increases with decreasing Si content down to x = 0.94. The yield stress of the GeSi alloys is dependent on the composition, being proportional to x(1 – x). The strengthening mechanism in alloy semiconductors is discussed.     

Preparation of SrAl2O4: Eu, Dy nanometer phosphors by detonation method

SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer phosphors were synthesized by detonation method. The particle morphology and optical properties of detonation soot that was heated at different temperatures (600–1100 °C) had been studied systematically by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicated SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer powders in monoclinic system (a = 8.442, b = 8.822, c = 5.160, β = 93.415) can be synthesized by detonation method, when detonation soot was heated at 600–800 °C. The particle size of SrAl₂O₄: Eu²⁺, Dy³⁺ is 35 ± 15 nm. Compared with the solid-state reaction and sol-gel method, synthesis temperature of the detonation method is lower about 500 and 200 °C respectively. After being excited under UN lights, detonation soot and that heated at 600–1100 °C can emit a green light.     

Hot deformation behavior of SiCp/AZ91 magnesium matrix composite fabricated by stir casting

The uniaxial compressive deformation behavior of a 10 vol.% SiC particulate reinforced AZ91 magnesium matrix composite (SiCp/AZ91) fabricated by stir casting is investigated at elevated temperature (250–400 °C). Peak stresses and flow stresses decrease as temperatures increase and strain rates decrease. The extent of dynamic recrystallization (DRX) becomes less as temperatures decrease at 250–350 °C or strain rates increase, and recrystallization occurs mainly within the intergranular regions rich of particles. Dynamic recrystallization accomplishes at 400 °C even at the strain rate of 1 s⁻¹. An analysis of the effective stress dependence on strain rate and temperature gives a stress exponent of n = 5 and a true activation energy of Q = 99 kJ/kJ. The value of Q is close to the value for grain boundary diffusion in Mg. It is concluded that the deformation mechanism of SiCp/AZ91 composite during hot compression is controlled by the dislocation climb.     

Effect of strain rate on the tensile behavior of a single crystal nickel-base superalloy

The effect of various strain rates on the tensile behavior of a single crystal nickel-base superalloy was studied. Single crystals with 0 0 1 crystal orientation were tested at 800 and 1000 °C under three kinds of strain rate of 10⁻³, 10⁻⁴ and 6 × 10⁻⁵ s⁻¹. The yield strength increased with the increase of strain rate, while the configuration of the stress–strain curves was independent of strain rate. Additionally, fracture surface was related to strain rate at two temperatures. At 800 °C the amount of cleavage surface was different at three strain rates, which resulted from the difference of activated slip systems. The elongation increased with the decrease of strain rate, which was influenced by the heterogeneous ductile deformation. At 1000 °C the difference of fracture surface was attributed to the microvoid at higher strain rate, while the γ/γ′ interfaces also played an important role at lower strain rate; elongation rate was independent of strain rate.     

Effect of temperature and strain rate on tensile behavior of ultrafine-grained aluminum alloys

Ultrafine-grained Al–4Y–4Ni and Al–4Y–4Ni–0.9Fe (at.%) alloys were synthesized by the consolidation of atomized powders and subsequent hot extrusion. The mechanical behavior of these two alloys has been studied by performing uniaxial tension tests ranging from room temperature to 350 °C. These alloys, with high volume fraction of second-phase particles, exhibited ambient temperature tensile strength ranging from 473 to 608 MPa and plastic elongation ranging from 6.7 to 9.6% at an initial strain rate of 1 × 10⁻³ s⁻¹. However, lower ductility was observed with decreasing strain rate at the intermediate temperature ranging from 150 to 250 °C for Al–Y–Ni–Fe alloys due to limited work hardening.     

Microstructure and superplasticity of laser welded Ti–6Al–4V alloy

In this paper laser beam welding (LBW) was used to join Ti–6Al–4V alloy as a pre-forming operation before superplastic deformation (SPF) process. Superplastic deformation behavior of laser welded Ti–6Al–4V alloy was investigated. The results indicated that the welded Ti–6Al–4V alloy had good superplasticity when deformed at temperature range of 870–920 °C and strain rate range of 10⁻³–10⁻² s⁻¹, and the elongation was 233–397%. The microstructure observation indicated that dynamic recrystallization happened in the weld bead, and the acicular structure of weld bead was transforming into equiaxed grains during tensile process.     

Effect of Mg17Al12 precipitates on the microstructural changes and mechanical properties of hot compressed AZ91 magnesium alloy

During hot compression, Mg₁₇Al₁₂ (β) precipitates show strong influence on the microstructural changes of 415 °C-24 h homogenized AZ91 alloy. When compressed at 300 °C and 350 °C, dynamic recrystallization (DRX) only occurs near grain boundaries with discontinuous β precipitate pinning at the newly DRXed grain boundaries. With increasing compression temperature and decreasing strain rate, the β-precipitating region expands; however, the amount of pinning precipitates decreases, resulting in increases in the DRX ratio and average DRXed grain size. With a compression ratio of only 50%, the specimen compressed at 350 °C and a strain rate of 0.2 s⁻¹ (designated 350 °C-0.2 s⁻¹ compressed specimen) shows an ultimate tensile strength (UTS) of 334 MPa, a 0.2% proof stress (PS) of 195 MPa and an enough elongation of 17.9%. After a subsequent aging treatment at 180 °C, due to the large number of β precipitates, the strength of the compressed specimens are further improved, and the specimen peak aged after compression at 400 °C and 0.2 s⁻¹ shows UTS of 364 MPa and PS of 248 MPa with a moderate elongation of 7.7%.     

Effect of heat treatment on the infrared absorption spectra of Sr-Na borosilicate glass

Internal modes of vibrations are studied here at different temperatures (27–800°C) and in the frequency range 200–4000 cm^–1 through heat treatment. The baseline method was used. The strong bands of SiO₄ tetrahedra in this glass show an increase in absorbance at high temperature (600–800°C). The deformation of SiO₄ tetrahedra is investigated. This is found to depend on the ionic radius of the divalent metal oxide introduced, and the coordination number of the cation. Also from a study of the temperature dependence of the relative integrated intensity of the modes 600–800 and 850–1450 cm^–1, the relaxation time and rotational energy barrier of the glasses selected indicate that the glassy phases are transformed to crystalline phases at 500°C.     

Bending strength and effective modulus of atmospheric ice

Bending strength and the effective modulus of atmospheric ice accumulated in a closed loop wind tunnel at temperatures − 6 °C, − 10 °C and − 20 °C with a liquid water content of 2.5 g/m³ have been studied at different strain rates. More than 120 tests have been conducted. Ice samples, accumulated at each temperature, have been tested at the accumulation temperature. In addition, tests have been performed at temperatures of − 3 °C and − 20 °C, for the ice accumulated at − 10 °C. These tests showed a clear dependency of bending strength of atmospheric ice on test temperature at low strain rates. Strain rate effects are implied because the spread in bending strength for the different temperatures diminishes as strain rate increases. The results also reveal that, in most cases, the effective modulus of atmospheric ice increases with increasing strain rate. The bending strength of atmospheric ice accumulated at − 10 °C has been found to be greater than that of ice accumulated at − 6 °C and − 20 °C. The results show that the effective modulus of ice accumulated at − 20 °C at higher strain rates is less than that of the two other types.     

Serrated flow behavior in a near alpha titanium alloy IMI 834

Serrated behavior of near alpha titanium alloy IMI 834 has been studied at elevated temperature from 400 °C to 475 °C. Serrations morphology was found as A type of locking serrations followed by B type serrations at 400 °C. E type of serrations has been observed at higher strains at 425 °C. B type and unlocking serrations of C_A type at 450 °C and again A and C_B type serrations were found at 475 °C. In strength parameters, anomalous tensile behavior was found in the variation of tensile strength and yield strength with test temperature in the temperature range between 400 °C and 475 °C. However, the variation of normalized flow stress showed regions I–III with test temperature. Regions I and III correspond to normal tensile behavior and region II corresponds to anomalous tensile behavior. Blue brittle temperature of IMI 834 was attributed at 450 °C by confirming minimum ductility of 8.2%. In present study, a different approach has been adopted to show the change in deformation behavior during serrated region called as abrupt change in strain path. Maximum irregularity in flow behavior has been observed at 450 °C and 475 °C. Room temperature fractographic features showed transgranular features whereas mixed ductile and cleavage fracture has been observed in the temperature range between 400 °C and 475 °C. However, reverse slope behavior has been observed in the plot of critical strain versus test temperature at 450 °C, which could be due to silicide precipitation. In the present study, interaction of dislocations with interstitial/substitutional solutes is responsible for dynamic strain aging in IMI 834.     

Microstructure and mechanical properties of an HfB2 + 30 vol.% SiC composite consolidated by spark plasma sintering

An ultra-high-temperature HfB₂–SiC composite was successfully consolidated by spark plasma sintering. The powder mixture of HfB₂ + 30 vol.% β-SiC was brought to full density without any deliberate addition of sintering aids, and applying the following conditions: 2100 °C peak temperature, 100 °C min⁻¹ heating rate, 2 min dwell time, and 30 MPa applied pressure. The microstructure consisted of regular diboride grains (2 μm mean size) and SiC particulates evenly distributed intergranularly. The only secondary phase was monoclinic HfO₂. The incorporated SiC particulates played a key role in enhancing the sinterability of HfB₂. Flexural strength at 25 °C and 1500 °C in ambient air was 590 ± 50 and 600 ± 15 MPa, respectively. Fracture toughness at room temperature (RT) (3.9 ± 0.3 MPa √m) did not decrease at 1500 °C (4.0 ± 0.1 MPa √m). Grain boundaries depleted of secondary phases were fundamental for the retention of strength and fracture toughness at high temperature. The thermal shock resistance, evaluated through the water-quenching method, was 500 °C.     

Partially alloyed filler sheet for brazing of Ti and its alloys fabricated by spark plasma sintering method

Partially alloyed filler metals in the form of powders and laminated foils were used for the brazing of Ti and Ti alloys to lower the manufacturing cost. In this study, by using a raw elemental powder mixture, a multi-component filler sheet with a nominal composition of 37.5Ti–37.5Zr–15Cu–10Ni was fabricated using a Spark Plasma Sintering (SPS) machine in the temperature range from 650 °C to 785 °C for 1 min. As the sintering temperature was increased from 650 °C to 750 °C, the bending strength of the sheets tended to rise, but the bending strength at 785 °C was drastically reduced. The melting range of the sheets became similar to that of the as-cast alloy. The sheets sintered at 750 °C showed the highest bending strength of 259 MPa, which was much higher than that of the as-cast material, and the melting range of this sheet was from 800 °C to 852 °C. The relatively high strength of the sheet was due to the remaining elemental powders such as Ti or Zr, but the brittle intermetallics, such as Ti₂Cu and (Ti,Zr)₂Ni Laves phases, formed in the sheet during the sintering process deteriorated its mechanical strength. The partially developed eutectic phase between the remaining Ti or Zr powder caused the sheet to exhibit melting behavior similar to that of the as-cast alloy. The brazability of the sheet sintered at 750 °C was examined with commercially pure Ti at 870 °C for 5–60 min. The tensile strength of the Ti joint brazed for 30 min was 431 MPa, which was close to that of the base metal.