Effect of consolidating temperature on strengthening mechanism in Fe–Cu alloy from rapidly solidified powder

Abstract

The strengthening mechanism of Fe-Cu alloy manufactured from rapidly solidified powder was investigated. Powders of Fe-Cu with copper content ranging from 0.5 to 5 wt-% were prepared by high pressure water atomisation and consolidated by groove rolling at 973, 1073 or 1273 K. Analysis by X-ray diffraction (XRD) and electron probe microanalysis (EPMA) were carried out to evaluate the resulting structures. The microstructures were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Yield stress under tensile loading and hardness after aging were measured. The copper states in consolidated specimens were determined based on the results, and the states were correlated to the mechanical properties of the specimens. At each of the consolidating temperatures, the yield stress increased with an increase in copper content. However, the strengthening mechanism differed according to the temperature. Specimens consolidated at 973 and 1073 K were strengthened by microstructure refinement,whereas precipitation hardening was the main strengthening mechanism in specimens consolidated at 1273 K.     

Microstructures in rapidly solidified Mg–Mn

Abstract

A Mg–2 wt-%Mn alloy has been rapidly solidified by melt spinning to produce ribbons 200–300 μm thick, 3–10 mm wide, and up to 0·3 m long. The solidification microstructure has been analysed by optical microscopy, conventional and scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and focused-probe microdiffraction. The rapid solidification resulted in Mg grain sizes between 10 and 20 μm. In regions extending from the substrate and partly through the thickness, the solidification structure was cellular with cell spacings between 1 and 2 μm. This structure exhibited an enriched Mn content between cells, an unusual segregation pattern for a peritectic system. The cell boundaries were decorated by rod-shaped particles, 10–20 nm long, of the metastable phase β-Mn. Outside the cellular region the solidification structure was similar to that of conventionally cast material. There were some coarse β-Mn particles of ~ 0·1 μm dia., probably as a result of precipitation from the melt.

MST/134     

Formation of hypoeutectic microstructure in a rapidly solidified Al–5 wt-%Sr alloy

Abstract

The microstructure and thermal analysis of the melt spun Al-5 wt-%Sr alloy have been investigated using X-ray diffraction, TEM, and differential scanning calorimetry (DSC). The experimental results show that rapid solidification makes the eutectic composition shift to a higher Sr content exceeding 5 wt-%Sr. The microstructure of the melt spun Al-5Sr alloy is hypoeutectic and composed of primary α-Al cells and the α-Al/Al₄Sr eutectic; quite different from that of the ingot like alloy comprising coarse primary Al₄Sr phase embedded in the eutectic. In the melt spun Al-5Sr alloy, some areas comprise equiaxed or elongated α-Al cells with intercellular irregular α-Al/Al₄Sr eutectic. Moreover, some areas fully comprise coupled α-Al/Al₄Sr eutectic. The eutectic Al₄Sr phase is lamellar strip like or vermiform in morphology. The size of the eutectic Al₄Sr phase is less than 50 nm in width. Furthermore, the very fine microstructure of the melt spun Al-5Sr alloy has a marked effect on the DSC trace in heating process.     

Effect of consolidation temperature on mechanical properties of rapidly solidified Al–7Mg–1 Zr alloy

Abstract

The mechanical properties achieved via the extrusion of non-degassed billets prepared from an inert gas atomised powder of nominal composition Al–7Mg–lZr are reported. The alloy was extruded over the temperature range 350–550°C and the tensile mechanical properties and plane strain fracture toughness were evaluated. It was found that the yield strength remained fairly constant over the entire temperature range, with only a small decrease in strength observed at the highest extrusion temperature. The strength could be related to microstructure using standard models for solid solution, dispersoid, and substructural strengthening mechanisms, and the last was found to make the greatest contribution. The sensitivity of strength to subgrain size was found to be nearly three times higher than that for pure Al. The optimum combination of strength and fracture toughness was obtained for extrusion at 500°C (yield strength 400 MN m^?2; T–L K_Iv 21 MN m^?3; elongation 20%). The poor values of K_lv obtained at other temperatures were attributed to coarse dispersoids (highest extrusion temperature), undeformed powder particles (lowest extrusion temperature), and inhomogeneous dispersoid distributions (intermediate temperatures). It is concluded that extrusion process control plays an important role in determining the mechanical properties of consolidated rapidly solidified powders. Considering the excellent ductility and toughness obtained, vacuum degassing before extrusion may not be essential in the processing of inert gas atomised powders of a non heat treatable composition.

MST/1721     

Effect of extrusion parameters on properties of rapidly solidified Al–Mg powder alloys

Abstract

Three rapidly solidified Al–Mg powder alloys have been consolidated by means of cold compaction followed by hot extrusion. The extrusion conditions of temperature, reduction ratio, and ram speed were varied, and it was observed that the mechanical properties of the extrudates were strongly process related. Relationships between properties and the temperature compensated strain rates during extrusion have been established. These alloys have strength/density properties superior to the strongest conventional ingot cast alloys. Good fracture toughness has been recorded in the Al–7 Mg alloy and all three alloys possess good resistance to stress corrosion cracking.

MST/498     

Wear behaviour of 85Al–10La–5Ni alloy prepared by powder metallurgy

Abstract

The dry wear behaviour of 85Al–10La–5Ni (at.-%) alloy hot pressed has been studied. The result shows that 85Al–10La–5Ni alloy possessed excellent wear resistance. The wear resistance of the alloy pressed at 773 K is three times as high as that of the A355 aluminium alloy. The fine high hardness intermetallic compounds contribute to the wear resistance of the alloy.     

Microstructure development and mechanical properties of rapidly solidified Ti–Fe and Ti–Fe–Bi alloys

Even though rapidly solidified Ti–Fe eutectic alloys may achieve good mechanical strength, increase in ductility is already a task to be accomplished. Addition of tin and arrangements of nano- and ultrafine-grain metallic materials have been shown as potential alternatives to overcome such drawback. Also, to address this problem, it seems that alternative alloy chemistries and processing routes must be adopted when manufacturing Ti-based alloys. In the present investigation, Ti–26 wt.%Fe (Ti–24.5 at.%Fe) and Ti–20 wt.%Fe–3 wt.%Bi (Ti–18 at.%Fe–0.7 at.%Bi) alloys have been prepared in a stepped copper mold using centrifugal casting. The as-cast Ti–Fe(–Bi) microstructures were formed by equiaxial arrangements of cells. Finer cell spacing (λ_c) was associated with the Ti–20 wt.%Fe–3 wt.%Bi alloy. The results include cell spacing measurements, segregation profile by X-ray fluorescence (XRF), uniaxial compression tests, optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A wide variation on the scale of the microstructure was noted especially in the case of the Ti–26 wt.%Fe alloy with the λ_c varying from 11−30 μm. This is due to the different cooling conditions of each diameter along the as-cast rod. Hall–Petch type equations are proposed relating σ_max to λ_c. Bi was dissolved in the β-Ti solid solution as well as TiFe compound formed in the cellular structure of the Ti–20 wt.%Fe–3 wt.%Bi.     

Effect of Ce on microstructures and mechanical properties of rapidly solidified Mg–Zn alloy

Abstract

The rapidly solidified (RS) Mg–Zn based alloys with Ce addition were produced via atomising the alloy melt and subsequent splat quenching on the water cooled copper twin rollers in the form of flakes. The effects of Ce additions on the microstructures, phase compositions, thermal stability and isochronal age hardening behaviour of the RS Mg–Zn alloy were systematically investigated. The RS Mg–6Zn alloy is characterised by fine grains in the size of 6–10 μm and is composed of α-Mg, Mg₅₁Zn₂₀ and a small quantity of MgZn₂ and Mg₂Zn₃ phases. With the increment of Ce, the microstructures of the alloys are refined, and the volume fractions of dispersions are increased remarkably. The stable intermetallic compounds, i.e. the Mg_xZn_yCe_z ternary phases, are formed in the RS Mg–Zn–Ce alloys at the expense of the Mg₅₁Zn₂₀ phases, which leads to the enhanced thermal stability of the alloys, especially for the Mg–6Zn–5Ce alloy. In the alloy, the atomic percentage ratio of Zn/Ce in the Mg_xZn_yCe_z phase is close to two, and the maximum hardness is 91·5±7 HV after annealing at 200°C for 1 h. However, the age hardening behaviour of the alloys decreases with the increment of Ce, and the main reason is discussed.     

Study of rapidly solidified Cu–Cr–RE alloys

Electrical engineering materials of Cu–Cr–RE have been made using the technology of rapid solidification, composite green compacts, extrusion and so on. By means of the analysis of optical metallographs, electron microscopy, physical and mechanical properties as well as electrical properties, and the examining of the hardness, softening temperature, etc. the authors selected Cu–Cr–Y alloy, which has excellent comprehensive properties. The authors have also made a deep study of the chromium and yttrium elements, which affect the structure, the recrystallization temperature, the strength at room and high temperature, the resistivity and contact resistance, and have also compared the properties of the Cu–Cr and Cu–Cr–Y alloy. The results show that rapidly solidified technology and added rare-earth elements not only enhance the fine grain boundary strengthening, but also the second phase strengthening. Cu/Cu–Cr–Y composite material improves the thermal stability and thermal endurance, and also maintains a better electrical conductivity and thermal conductivity.     

Study of rapidly solidified Cu–Cr–RE alloys

Electrical engineering materials of Cu–Cr–RE have been made using the technology of rapid solidification, composite green compacts, extrusion and so on. By means of the analysis of optical metallographs, electron microscopy, physical and mechanical properties as well as electrical properties, and the examining of the hardness, softening temperature, etc. the authors selected Cu–Cr–Y alloy, which has excellent comprehensive properties. The authors have also made a deep study of the chromium and yttrium elements, which affect the structure, the recrystallization temperature, the strength at room and high temperature, the resistivity and contact resistance, and have also compared the properties of the Cu–Cr and Cu–Cr–Y alloy. The results show that rapidly solidified technology and added rare–earth elements not only enhance the fine grain boundary strengthening, but also the second phase strengthening. Cu/Cu–Cr–Y composite material improves the thermal stability and thermal endurance, and also maintains a better electrical conductivity and thermal conductivity.     

Effect of Cr addition on microstructures and nanohardness of rapidly solidified Ti–48Al alloy

Abstract

In this present work, the microstructure and nanohardness of rapidly solidified Ti–48 at-%Al alloy with various Cr additions were experimentally investigated using the single roller melt spinning technique. Ti–48Al alloy with various Cr additions were prepared by arc melting for comparison. In the arc melted alloy, the volume fraction of the interdendritic γ phase decreases, and the lamellar structure and the B2 phase increase with the increase in Cr addition. After rapid solidification, the Ti–48Al alloy consists of the γ phase and α₂ the phase, with the γ phase as the matrix. The α₂ phase exists as particles or in lamellar structure, which embed in the matrix. With 2 at-%Cr addition, the alloy ribbons mainly consist of equiaxial α₂ grains and small particles of the B2 phase, with few lamellar structures occasionally found at the triple grain boundary. Increasing Cr content to 4 at-%, the grain size of the B2 phase increases, and lamellar structures disappear. The change in nanohardness was discussed based on the microstructural observations. It shows a certain increase in the nanohardness as Cr content increases to 4 at-%. This can be attributed to the changes in the microstructures.     

Influence of silver additions on electrical, mechanical and structures properties of rapidly solidified Sn–0.7%Cu alloy from melt

The eutectic alloy Sn_99.3-xCu_0.7Ag_x has been examined as one of the lead free solder alloys. Melting point, electrical resistivity, internal friction, elastic moduli, microhardness and the microstructure of the Sn_99.3Cu_0.7, Sn_95.8Cu_0.7Ag_3.5 and Sn_95.3Cu_0.7Ag₄ rapidly solidified lead free solder alloys have been investigated. The examined physical properties are improved by increasing silver contents in the studied lead free solder alloys. These improved properties indicate that these alloys are adequate for low temperature soldering applications.     

Effect of consolidation route on structure and property control in rapidly solidified Al–Cr–Zr–Mn povvder alloy for high temperature service

Abstract

In this paper the authors describe a new rapidly solidified alloy which is capable of meeting the projected requirements of the aerospace industry. Initial studies using splat quenched particulates were carried out on the Al–Cr–Zr system. Microhardness tests indicated that these alloys age–hardened between 350 and 400°C and showed excellent thermal stability. Further alloy development and studies of fabrication behaviour were carried out using air atomized powder. Powders were consolidated by either conventional or hydrostatic extrusion. Microstructural changes during fabrication were identified and correlated with mechanical property data. The alloy can achieve the requirements of the aerospace industry provided microstructural development is controlled during fabrication.

MST/233     

Damping behaviour and mechanical properties of rapidly solidified Al–Fe–Mo–Si/Al alloys

In order to develop a new high damping aluminium alloy with strength and toughness for advanced aircraft structure application, rapidly solidified (RS) Al–Fe–Mo–Si/Al alloys were synthesized. The damping behaviour, mechanical properties and microstructures of the alloys were studied. Results showed that the damping capacities of RS Al–Fe–Mo–Si/10–15% Al alloys are stable between 7.0–10.0×10-3 at room temperature, which almost reach the high damping threshold, 10.0×10-3. At lower frequency (0.1–10 Hz) the damping capacity is decidely frequency and temperture dependent above 50°C, with lowest frequency and highest temperature resulting in the highest less factor. It was noted that mechanical properties of the Al–Fe–Mo–Si/10–15% Al alloys are both excellent at room temperature (b=536–564 MPa, =7.2–11.4%) and at elevated temperature (250°C: b=295–324 MPa). Analysis of microstructures reveal that the damping capacity arises from deformation of the pure Al areas, and strength at elevated temperature from the dispersion strengthening of intermetallic phase. © 1998 Chapman & Hall     

Influence of atomized powder size on microstructures and mechanical properties of rapidly solidified Al–Cr–Y–Zr aluminum alloys

Rapidly solidified powders of Al–5.0Cr–4.0Y–1.5Zr (wt%) were prepared by using a multi-stage atomization-rapid solidification powder-making device. The atomized powders were sieved into four shares with various nominal diameter level and were fabricated into hot-extruded bars after cold-isostatically pressing and vaccum degassing process. Influence of atomized powder size on microstructures and mechanical properties of the hot-extruded bars was investigated by optical microscopy, X-ray diffraction, transmission electronic microscopy with EPSX and scanning electron microscopy. The results show that the fine atomized powders of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy attains supersaturated solid solution state under the exist condition of multi-stage rapid solidification. With the powder size increasing, there are Al₂₀Cr₂Y (cubic, a = 1.437 nm) and Ll₂ Al₃Zr (FCC, a = 0.407 nm) phase forming in the powders, and even lumpish particles of Al₂₀Cr₂Y appearing in the coarse atomized powders, as can be found in the as-cast master alloy. Typical microstructures of the extruded bars of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy can be characterized by fine grain FCC α-Al matrix with ultra-fine spherical particles of Al₂₀Cr₂Y and Al₃Zr. But a small quantity of Al₂₀Cr₂Y coarse lumpish particles with micro-twin structures can be found, originating from lumpish particles of the coarse powders. The extruded bars of rapidly solidified Al–5.0Cr–4.0Y–1.5Zr aluminum alloy by using the fine powders eliminated out too coarse powders have good tensile properties of σ_0.2 = 403 MPa, σ_b = 442 MPa and δ = 9.4% at room temperature, and σ_0.2 = 153 MPa, σ_b = 164 MPa and δ = 8.1% at high temperature of 350 °C.     

Welding of rapidly solidified Alloy 8009 (Al–8·5Fe–1·7Si–1·3V): preliminary study

Abstract

Alloy 8009 is a rapidly solidified, dispersion strengthened Al–8·5Fe (wt-%) alloy designed for high temperature (up to 400°C) aerospace applications. Both fusion and solid state joining techniques were shown to produce bonds. Fusion techniques destroyed the base metal microstructure with primary Fe₃Al, loss of solute, formation of larger aluminium grains, and the formation of grain boundary FeAl₃ and intermetallics enriched with silicon and vanadium. Solid state friction stir welding did not cause a significant modification to the dispersoid population but there was a loss of solute to dispersoid/matrix interfaces.

MST/3500     

Extrusion processing of Al–Li–Mg–Zr alloy

Abstract

The hot deformation behaviour of an Al–Li–Mg–Zr alloy was characterised in hot torsion and extrusion. The alloy was found to have similar hot ductility to existing high strength aluminium alloys, but this could be maintained at higher temperatures. Billets were extruded over a range of process conditions and a limit diagram was constructed for surface cracking. All the extrusions were found to be partially recrystallised after deformation, but the volume fraction of recrystallisation was a strong function of billet temperature and extrusion ratio. In addition, the unrecrystallised areas contained a recovered substructure where the subgrain size was inversely proportional to the temperature compensated strain rate. The as extruded structure was retained during solution treatment and as a result final mechanical properties were strongly dependent on the extrusion conditions. The use of high billet temperatures and low extrusion ratios gave the best combination of strength and toughness.

MST/839     

Extrusion of vapour deposited Al–7·5Cr–1·2Fe (wt-%) alloy (RAE Alloy 72)

Abstract

Techniques and equipment were developed for the extrusion of vapour deposited RAE Alloy 72. The alloy was extruded at temperatures from 300 to 420°C and extrusion ratios from 2:1 to 25:1. Room and elevated temperature strengths and smooth S–N (stress–number of cycles to failure) fatigue properties were determined for a range of extrusions. The best extrusions gave room and elevated temperature strengths that were comparable to those of rapidly solidified aluminium alloys. The fatigue strength/tensile strength ratio of >0·5 was higher than would be expected for an aluminium alloy.

MST/1350     

Extrusion of AI–Zn–Mg–Cu–Zr alloys

Abstract

Four aluminium alloys of different zinc/magnesium ratio have been studied under various extrusion conditions. The alloys were cast in steel book moulds and subjected to initial thermomechanical treatments. Studies were made of hot extrusions and cold hydrostatic extrusions and in each case the changes in the extrusion parameters were analysed. An attempt has been made to explain some of the extrusion defects which appeared in various extruded sections. The extrusion speed was found to be crucial, since sections developed surface cracks at higher speeds. The extrusion speed was also found to vary inversely with the extrusion ratio, with higher speeds at low ratios. A well defined solute–depleted weld zone was observed on each of the four faces of a square tube extruded using a porthole die. Thermal treatment was not found to improve this weak weld zone. Tubes extruded using a floating-mandrel die withstood pressure testing up to 550 MPa.

MST/43     

Evolution of microstructure in laser clad Fe–Cr–Mn–C alloy

Abstract

The laser surface cladding technique was used to form in situ Fe–Cr–Mn–C alloys on AISI 1016 steel substrate. In this process, mixed powders containing Cr, Mn, and C in the weight ratio 10: 1 : 1 were delivered using a screw feed, gravity flow, carrier gas aided system into the melt pool generated by a 10 kW CO₂ laser. This technique produced an ultrafine microstructure in the clad alloy layer. The microstructure of the laser surface clad region was investigated by optical, scanning and transmission electron microscopy, and X-ray microanalysis techniques. Microstructural study showed a high degree of grain refinement and an increase in solid solubility of alloying elements which, in turn, produced a fine distribution of complex types of carbide precipitates in the ferrite matrix because of the high cooling rate. An alloy of this composition does not show any martensitic transformation or retained austenite phase.

MST/356