Design and deformation behavior of high strength Fe–Mn–Al–Cr–C duplex steel

The influence of cold rolling reduction on microstructures and mechanical properties at room temperature of the duplex Fe–28Mn–7Al–5Cr–0.3C steel was investigated. In the Fe–28Mn–7Al alloy system, the duplex microstructure was obtained by lowering the carbon content to about 0.3 wt.%. The steel was austenito-ferritic with a low to moderate stacking fault energy. Two thermomechanical cycles were performed, which included cold rolling/annealing at 1100 °C, and cold rolling/annealing at 1100 °C/cold rolling/annealing at 1000 °C.The effects produced by cold rolling on the duplex steel were grain refinement and different strain-induced marks within the ferrite and austenite phases. They were easily observed within the austenite phase at a relatively smaller reduction than within the ferrite phase. Mechanical twinning plays a dominant role within the austenite phase during deformation at room temperature, resulting in extreme mechanical properties. No edge or longitudinal cracks were observed during cold rolling of the duplex steel.     

Grain growth behaviour and consolidation of ball-milled nanocrystalline Fe–10Cr alloy

Nanocrystalline iron–chromium alloys may provide considerable corrosion resistance, even at low chromium contents. However, processing of such alloys could be a challenge. This paper describes successful synthesis of nanocrystalline Fe–10%Cr alloy by ball-milling route. In the absence of suitable hot compaction facility, the alloy powder could be successfully compacted close to the desired density, by employing a step of prior annealing of the powder. Grain growth behaviour of Fe–10%Cr nanocrystalline alloy was investigated at 500, 600 and 700 °C. At 500 °C, no appreciable grain growth was observed, after the initial grain growth. However, sudden and rapid grain growth was observed after 90 min at 600 °C, and 30 min at 700 °C.     

Experimental study on the plastic deformation and densification characteristics of some sintered and heat treated low alloy powder metallurgy steels

Sintered low alloy steels containing the alloying elements molybdenum, copper and titanium were synthesised through powder metallurgy route from mixed elemental powders to yield the compositions: Fe–0.5% C, Fe–0.5% C–2% Cu, Fe–0.5% C–2% Mo and Fe–0.5% C–2% Cu–2% Mo–2% Ti. Green cylindrical compacts were made using a 1000 kN hydraulic press using suitable cylindrical die-punch combination. The ceramic coated cylindrical preforms were sintered at 1000 ± 10 °C in a muffle furnace for a period of 120 min. After sintering, the preforms were subjected to different heat treatment processes, namely, heating to 900 °C, soaking for 60 min and quenching in air or oil or cooled inside the furnace. The heat treated preforms were subject to axial upsetting deformations, at various applied loads and their densification behaviours were compared. The influence of various heat treatment processes on deformation and densification of the alloys was studied and correlated with their microstructures. The plain carbon steel preforms were observed to respond well to the three heat treatment cycles by way of exhibiting the highest levels of densification and plastic deformation. However, both alloy addition and heat treatment have led to a reduction in densification and deformation of the alloy steel preforms. Presence of titanium carbide particulates in the microstructure of the Ti-alloyed steel has played a significant role in reducing the densification as well as deformation. The basic ferritic–pearlitic microstructure of Fe–0.5% C steel has essentially promoted the largest deformation levels coupled with higher densification.     

Structure, microstructure and mechanical properties of PM Fe–Cu–Co alloys

Fe–Cu–Co alloys are the new generation of metal matrix for diamonds in powder metallurgy processed cutting tools. These alloys were created with the purpose of reducing the cobalt content in diamond tools. Nevertheless, little have been published, once this is a matter of industrial interest. In this work, samples of Fe–(15-30-45-60)wt.%Cu–20 wt.%Co alloys were processed by cold pressing at 350 MPa, followed by sintering at 1150 °C/25 min/10⁻² mbar. Structures formed during sintering were studied by XRD and EDS. Micro-structural aspects were observed by SEM. Densification, hardness and wear tests were also performed. The alloy Fe–60 wt.%Cu–20 wt.%Co presented the best global results, suitable for use in diamond cutting tools.     

Nanoscale dynamic wetting and spreading of molten Ti alloy on 6H–SiC

We have investigated nanoscale features at the reactive wetting front of the molten Ag–27.4 wt.% Cu–4.9 wt.% Ti on 6H–SiC using video movies recorded in situ on a high-temperature stage of a high-resolution transmission electron microscope and also proposed a model of a chemical reaction at each tip. One of the features of reactive wetting and spreading at 1073 K in 4 × 10⁻⁵ Pa was the discontinuous motion of the tip, and the halting time depended on the thickness of an amorphous Si–O layer on SiC, which can be explained by the time needed for the decomposition of the layer by Ti atoms to form TiC nanoparticles since Ti atoms in the molten alloy sufficiently rapidly diffuse to the tip on the SiC surface. Molten Ti and TiC nanolayers preceded the Ti₅Si₃ nanolayer at the tip. The reaction required to form the TiC nanolayer is also the rate-determining step for spreading. The contact angle of the tip increased up to 60–80° when the tip halted, whereas the tip decreased down to 10° on the nonbasal plane and 20° on the basal plane of SiC when it traveled rapidly. The high traveling angle of the molten tip on the basal polar plane of SiC indicates a high interfacial energy between Ti and SiC(0 0 0 1).     

Combined effect of special grain boundaries and grain boundary carbides on IGSCC of Ni–16Cr–9Fe–xC alloys

Susceptibility to intergranular stress corrosion cracking in Ni–16Cr–9Fe–xC alloys in 360°C primary water is reduced with increasing fraction of special grain boundaries, i.e. coincident site lattice boundaries (CSLB) and low angle boundaries, and grain boundary carbides. Intergranular stress corrosion cracking (IGSCC) was investigated using interrupted constant extension rate tensile tests in a primary water environment at 360°C. Thermal–mechanical treatments were used to increase the fraction of special boundaries from approximately 20–25% to between 30 and 40%. In a carbon-doped heat, further heat treating was used to precipitate grain boundary carbides preferentially on high-angle boundaries (HAB). Orientation imaging microscopy was used to determine the relative grain misorientations and scanning electron microscopy (SEM) was used to identify specific grain boundaries after each interruption. After each strain increment, the same regions in each sample were examined for cracking. Results showed that irrespective of the microstructure condition, CSLBs always cracked less than HABs. Results also showed that IGSCC is reduced with increasing solution carbon content, and for the same amount of carbon in solution, the addition of grain boundary carbides reduced IGSCC still further. The best microstructure was the one consisting of an enhanced CSLB fraction and chromium carbides precipitated preferentially on high-angle boundaries.     

Wetting of pure aluminum and selected alloys on polycrystalline alumina and sapphire

Using a modification of the dispensed drop method to measure true contact angles of readily oxidizing metals and alloys, the wettability of polycrystalline alumina and A-plane sapphire by pure aluminum and selected aluminum alloys was investigated. The experiments were performed under high vacuum in a horizontal tube furnace. The experimental setup produces a sessile drop free of its natural surface oxide layer minimizing flight time of the drop, and maintaining a drop impingement on the substrate.The experiments showed that there is no significant difference in the wettability of alumina and sapphire by aluminum as well as Al–11.5Si, Al–1Mg and Al–7Cu. On both substrates, aluminum shows a strong increase in contact angle well into the non-wetting regime just above the melting point. The wetting behavior of Al–7Cu on both substrates is slightly but significantly reduced in comparison to pure aluminum. The contact angles of Al–1Mg and Al–11.5Si remain rather constant between the respective liquidus temperatures of the alloys and 800 °C with θ (Al–1Mg) < θ (Al–11.5Si). Only Al–7Cu above 730 °C achieves the contact angle interval of 70–86° suggested to be most beneficial in terms of aluminum foam stabilization.     

Effects of thermo-mechanical processing and trace amount of carbon addition on tensile properties of Cu–2.5Fe–0.1P alloys

The effects of thermo-mechanical processing, including intermediate aging treatment and/or solution heat treatment, and a trace amount of carbon (C) addition were studied on tensile behavior of Cu–2.5Fe–0.1P alloys. In this study, Cu–2.5Fe–0.1P alloy sheets without and with a carbon content of 0.05 wt.% were cast and subsequently rolled and thermo-mechanically treated following various processing routes. The introduction of intermediate aging treatment between cold rolling improved the tensile strength of Cu–2.5Fe–0.1P alloys. Solution heat treatment prior to aging was proved to be detrimental on the tensile strength, probably due to recovery and recrystallization causing the complete loss of work hardening during previous cold rolling. The present study also suggested that two-step aging is more effective in improving the strength of Cu–2.5Fe–0.1P alloys than one-step aging. The effect of C addition on improving the tensile strength of Cu–2.5Fe–0.1P alloys was real but marginal, probably due to the limited solubility of C in Cu–2.5Fe matrix. The effects of intermediate heat treatments between cold-rolling processes on tensile properties of Cu–2.5Fe–0.1P specimens with and without C addition are discussed based on optical, scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs, and SEM fractographs.     

Wetting and brazing of stainless steels by copper–silver eutectic

The wetting of stainless steels by Cu–Ag-based alloys was studied by the sessile drop and dispensed drop techniques in high vacuum at 800–900 °C. Experiments were performed by varying the steel type, composition of the Cu–Ag-based alloy and furnace atmosphere. The results were used to determine the processes controlling the wetting and brazing of these important technological materials.     

Solidification microstructures and mechanical properties of high-vanadium Fe–C–V and Fe–C–V–Si alloys

Fe–C–V and Fe–C–V–Si alloys of various C, V and Si compositions were investigated in this work. It was found that the phases present in both of these alloy systems were alloyed ferrite, alloyed cementite, and VC_x carbides. Depending on the alloy composition the solidified microstructural constituents were granular pearlite-like, lamellar pearlite, or mixtures of alloyed ferrite + granular pearlite-like or granular pearlite-like + lamellar pearlite. In addition, it is shown that in Fe–C–V alloys the C/V ratio influences (a) the type of matrix, (b) the fraction of vanadium carbides, f_v and (c) the eutectic cell count, N_F. In Fe–C–V alloys, a relationship between the alloy content corresponding to the eutectic line was experimentally determined and can be described by where C_e and V_e are the carbon and vanadium composition of the eutectic. Moreover, in the Fe–C–V alloys (depending on the alloy chemistry), the primary VC_x carbides crystallize with non-faceted or non-faceted/faceted interfaces, while the eutectic morphology is non-faceted/non-faceted with regular fiber-like structures, or it possesses a dual morphology (non-faceted/non-faceted with regular fiber-like structures + non-faceted/faceted with complex regular structures). In the Fe–C–V–Si system, the primary VC_x carbides solidify with a non-faceted/faceted interface, while the eutectic is non-faceted/faceted with complex regular structures. In particular, spiral eutectic growth is observed when Si is present in the Fe–C–V alloys. In general, it is found that as the matrix constituent shifts from predominantly ferrite to lamellar pearlite, the hardness, yield and tensile strengths exhibit substantial increases at expenses of ductility. Moreover, Si additions lead to alloy strengthening by solid solution hardening of the ferrite phase and/or through a reduction in the eutectic fiber spacings with a decrease in the alloy ductility.     

Anisotropy of Young's modulus and tensile properties in cold rolled α′ martensite Ti–V–Sn alloys

Young's modulus and tensile properties of cold rolled Ti–8 mass% V and (Ti–8 mass% V)–4 mass% Sn alloy plates consisting of α′ martensite were investigated as a function of tensile axis orientation in this work. A single phase of α′ (hcp) martensite is obtained in Ti–8 mass% V and (Ti–8 mass% V)–4 mass% Sn alloys by quenching after solution treatment. By 86% cold rolling, acicular α′ martensite microstructures change into extremely refined dislocation cell-like structure with an average size of 60 nm, accompanied with the development of cold rolling texture in which the basal plane normal is tilted from the plate normal direction (ND) toward transverse direction (TD) at angles of ±49° for Ti–8% V alloy and ±46° for (Ti–8 mass% V)–4 mass% Sn alloy. No apparent anisotropy of Young's modulus (E) is observed for as-quenched Ti–8% V (E = 76–83 GPa) and (Ti–8% V)-4%Sn (E = 69–79 GPa). In contrast, Young's modulus increases with increasing angle from the rolling direction (RD) to TD for cold rolled Ti–8% V (E = 72–94 GPa) and (Ti–8% V)–4%Sn (E = 63–85 GPa). The observed anisotropy of Young's modulus can be reasonably explained in terms of the cold rolling α′ texture.0.2% proof stress and tensile strength are independent of tensile orientation for cold rolled Ti–8% V and (Ti–8% V)–4%Sn alloys. In contrast, larger elongation to fracture is obtained in specimens deviated by 30°, 45° and 60° from RD than by 0°, 75° and 90°. Scanning electron microscopy (SEM) fractographs reveal that quasi-cleavage-like fracture plane appears in 0° specimen of cold rolled Ti–8% V which shows brittle fracture and other specimens of cold rolled Ti–8% V and (Ti–8% V)–4%Sn alloys are fractured accompanied with necking and dimple formation. It is suggested from these results that brittle fracture is related to the activation of limited number of slip system and Sn addition leads to the activation of multiple slip systems.     

Microstructural investigations on as-cast and annealed Al–Sc and Al–Sc–Zr alloys

Al–Sc and Al–Sc–Zr alloys containing 0.05, 0.1 and 0.5 wt.% Sc and 0.15 wt.% Zr were investigated using optical microscopy, electron microscopy and X-ray diffraction. The phase composition of the alloys and the morphology of precipitates that developed during solidification in the sand casting process and subsequent thermal treatment of the samples were studied. XRD analysis shows that the weight percentage of the Al₃Sc/Al₃(Sc, Zr) precipitates was significantly below 1% in all alloys except for the virgin Al0.5Sc0.15Zr alloy. In this alloy the precipitates were observed as primary dendritic particles. In the binary Al–Sc alloys, ageing at 470 °C for 24 h produced precipitates associated with dislocation networks, whereas the precipitates in the annealed Al–Sc–Zr alloys were free of interfacial dislocations except at the lowest content of Sc. Development of large incoherent precipitates during precipitation heat treatment reduced hardness of all the alloys studied. Growth of the Al₃Sc/Al₃(Sc, Zr) precipitates after heat treatment was less at low Sc content and in the presence of Zr. Increase in hardness was observed after heat treatment at 300 °C in all alloys. There is a small difference in hardness between binary and ternary alloys slow cooled after sand casting.     

Effect of the long periodic stacking structure and W-phase on the microstructures and mechanical properties of the Mg–8Gd–xZn–0.4Zr alloys

Microstructures and mechanical properties of the Mg–8Gd–xZn–0.4Zr (x = 0, 1 and 3 wt.%) alloys, in the as-cast condition and the as-extruded condition, have been investigated. The results show that both the 14H long periodic stacking structure and the W-phase coexist together in the cast Zn-containing alloys. The volume fraction of the W-phase increases with increasing the addition of Zn. This phase is the crack source of the fracture. The 6H long periodic stacking structure is observed in the extruded Zn-containing alloys. The Mg–8Gd–1Zn–0.4Zr alloy exhibits the highest elongation, and the value of its elongation is 130% at 300 °C due to the refined microstructure. The W-phase plays an important role in improving the mechanical properties via pinning the movement of the grains at elevated temperature.     

Magnetic properties of Nd–Fe–B/FeMn multilayer films

[Nd–Fe–B(x nm)/FeMn(d nm)]_n thin films were deposited by magnetron sputtering on Si (100) substrates heated at 650 °C. The influence of the composition and thickness of FeMn layer on the structure and magnetic properties of Nd–Fe–B films are investigated. The Nd–Fe–B/FeMn multilayer films present an enhanced coercivity and a reduced saturation magnetization, in comparison with those of a Nd–Fe–B single layer. The coercivity of [Nd–Fe–B(x nm)/FeMn(5 nm)]_n films increases with increasing the period number of FeMn layer for the same thickness of magnetic layer, while the coercivity in [Nd–Fe–B(50 nm)/FeMn(5 nm)]_n films increases with decreasing the period number of Nd–Fe–B/FeMn bilayers. The coercivity H_c of about 17.2 kOe is achieved in the Nd–Fe–B(50 nm)/FeMn(5 nm) film.     

Microstructure and mechanical properties of Al–20Si–5Fe–2X (X = Cu, Ni, Cr) alloys produced by melt-spinning

Al–20Si–5Fe–2X (X = Cu, Ni and Cr) ribbons were produced by melt-spinning and consolidated by hot pressing at 400 °C for 60 min. The microstructure of the ribbons and the consolidated alloys was investigated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometry (XRD) method, and transmission electron microscopy (TEM). The hardness and compressive strength of the specimens at ambient and elevated temperatures were examined. The microstructure of the ribbons exhibited featureless and dendritic zones. Results of XRD and TEM showed formation of spherically shaped Si particles with an average diameter of 20 nm. Ultrafine Si (110–150 nm) and iron-containing intermetallic particles were noticed in the microstructure of the consolidated ribbons. An improved strength was achieved by alloying of Al–20Si–5Fe with Cu, Ni, and Cr. Nickel was found to be the most effective element in increasing the maximum stress, particularly at elevated temperatures.     

Interface interaction in the B4C/(Fe–B–C) system

The wetting behavior in the B₄C/(Fe–C–B) system was investigated in order to clarify the role of Fe additions on the sinterability of B₄C. Iron and its alloys with C and B react with the boron carbide substrate and form a reaction zone consisting of a fine mixture of FeB and graphite. The apparent contact angles are relatively low for the alloys with a moderate concentration of the boron and carbon and allow liquid phase sintering to occur in the B₄C–Fe mixtures. A dilatometric study of the sintering kinetics confirms that liquid phase sintering actually takes place and leads to improved mass transfer. A thermodynamic analysis of the ternary Fe–B–C system allows accounting for the experimental observations.     

The effect of sintering time on the densification and mechanical properties of a mechanically alloyed Cr–Mn–N stainless steel

Sintering is an essential stage in powder metallurgy, which affects the final microstructure and performance of the part. This study is concerned with the sintering and mechanical behaviors of Fe–18Cr–8Mn–0.9N stainless steel prepared from mechanically alloyed amorphous/nanocrystalline powders. The contribution of sintering time to the densification at 1100 °C is considered and a sluggish densification is found for the alloy. Furthermore, the correlation between the microstructure and mechanical properties of the fabricated porous parts is studied. It is found that the yield stress is affected by both porosity and the material’s intrinsic yield strength. Nonetheless, the effect of porosity on the overall hardness typically prevails over the effect of matrix hardness. Interestingly, even after sintering at 1100 °C for up to 20 h, the nanometric structure of the material is retained.     

Low-temperature compaction of Ti–6Al–4V powder using equal channel angular extrusion with back pressure

Equal channel angular extrusion (ECAE), with simultaneous application of back pressure, has been applied to the consolidation of 10 mm diameter billets of pre-alloyed, hydride–dehydride Ti–6Al–4V powder at temperatures ≤400 °C. The upper limit to processing temperature was chosen to minimise the potential for contamination with gaseous constituents potentially harmful to properties of consolidated product. It has been demonstrated that the application of ECAE with imposed hydrostatic pressure permits consolidation to in excess of 96% relative density at temperatures in the range 100–400 °C, and in excess of 98% at 400 °C with applied back pressure ≥175 MPa. ECAE compaction at 20 °C (back pressure = 262 MPa) produced billet with 95.6% relative density, but minimal green strength. At an extrusion temperature of 400 °C, the relative density increased to 98.3%, for similar processing conditions, and the green strength increased to a maximum 750 MPa. The relative density of compacts produced at 400 °C increased from 96.8 to 98.6% with increase in applied back pressure from 20 to 480 MPa, while Vickers hardness increased from 360 to 412 HV. The key to the effective low-temperature compaction achieved is the severe shear deformation experienced during ECAE, combined with the superimposed hydrostatic pressure.     

Creep deformation of Alloys 617 and 276 at 750–950 °C

Alloys 617 and 276 were subjected to time-dependent deformation at elevated temperatures under sustained loading of different magnitudes. The results indicate that Alloy 617 did not exhibit strains exceeding 1 percent (%) in 1000 h at 750, 850 and 950 °C when loaded to 10% of its yield strength (YS) values at these temperatures. However, this alloy was not capable of sustaining higher stresses (0.25YS and 0.35YS) for 1000 h at 850 and 950 °C without excessive deformation. Interestingly, Alloy 617 showed insignificant steady-state creep rate at 750 °C irrespective of the applied stress levels. Alloy 276 almost met the maximum creep deformation criterion when tested at 51 MPa–750 °C. Severe creep deformation of both alloys at 950 °C could be attributed to the dissolution of carbides and intermetallic phases remaining after solution annealing or precipitated during quenching.     

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.