Rapid Solidification Powder Metallurgy Research Articles

Development of Biomedical Mg–1.0Ca–0.5Zn–0.1Y–0.03Mn (at%) Alloy by Rapidly Solidified Powder Metallurgy Processing

We investigated the alloy composition of Mg-Ca-Zn alloys suitable for rapidly solidified powder metallurgy (RS PM) processing and tried to develop biomedical Mg-Ca-Zn RS PM alloys with high strength, high ductility, and high corrosion resistance. The alloy composition suitable for RS PM processing was Mg-1.0Ca-0.5Zn (at%) in ternary Mg-Ca-Zn alloys. An Mg-1.0Ca-0.5Zn RS PM alloy with combined additions of 0.1 at% Y and 0.03 at% Mn exhibited excellent performance with a tensile yield strength of 376±17 MPa, an elongation of 14.1±3.1%, and a corrosion rate of 0.46±0.04 mm·year-1 when immersed in HBSS, resulting in the achievement of our target properties. Especially the yield strength of the Mg-1.0Ca-0.5Zn-0.1Y-0.03Mn RS PM alloy developed in this study was higher than that of previously reported Mg-Zn-Ca(-Mn-Zr) or Mg-Ca-Zn(-Mn-Zr) ingot metallurgy (IM) alloys, which were produced by single extrusion, double extrusion or severe plastic deformation (SPD) of cast ingots.

Super‐High Strength Mg–7.5Al–0.8Zn Alloy Prepared by Rapidly Solidified Powder Metallurgy and Low Temperature Extrusion

In this work, Mg–7.5Al–0.8Zn alloy with super‐high tensile strength are fabricated by rapidly solidified powder metallurgy (RS/PM) and low temperature extrusion technology. By reducing extrusion temperature from 340 to 170 °C, the α‐Mg grains are significantly refined and numerous nanoscale β‐Mg17Al12 particles are obtained. The RS/PM alloy extruded at 170 °C possesses the lowest grain size of ≈550 nm. The nanoscale β‐phase particles stimulate the nucleation of dynamically recrystallized (DRXed) grains and restrain the growth of DRXed grains. The RS/PM alloy extruded at 170 °C exhibits mechanical properties with a tensile yield strength of 448 MPa, an ultimate tensile strength of 480 Mpa, and a microhardness of 137 HV. These excellent mechanical properties result from low temperature extrusion are mainly attributed to the ultra‐fine DRXed grains and the high‐density dislocations and subgrains.

Microstructure and mechanical properties of Al–5.5Fe–1.1V–0.6Si alloy solidified under near-rapid cooling and with Ce addition

Al–Fe–V–Si alloys were developed for use at elevated temperature and usually produced through a rapid solidification–powder metallurgy route. In this work, effort was made to produce the material via casting route. The studied alloys were cast under the condition of near-rapid cooling. The influence of Ce addition on microstructure and mechanical properties of near-rapid solidified alloys were investigated. The results indicate that the as-cast microstructure of Al–5.5Fe–1.1V–0.6Si alloy is significantly refined when the alloy was solidified under near-rapid cooling. Adding Ce results in the further refinement of intermetallic compound and the formation of an Al–V–Ce phase which replaces the primary phase Al13(Fe,V)3Si. The mechanical properties of the alloy are significantly improved by Ce addition: More than 70% increase in tensile strength and elongation is achieved by adding 1.00 wt% Ce to the alloy. It is concluded that near-rapid cooling and Ce addition are effective in improving mechanical properties of cast Al–5.5Fe–1.1V–0.6Si alloy.

Fabrication and characterization of nanocrystalline Al/Al12(Fe,V)3Si alloys by consolidation of mechanically alloyed powders

The aim of this study was to produce bulk nanocrystalline Al/Al12(Fe,V)3Si alloys by mechanical alloying (MA) and subsequent hot pressing (HP) of elemental powders. A nanostructured Al-based solid solution was formed by MA of elemental powders for 60 h. After HP of the as-milled powders at 550°C for 20 min, the Al12(Fe,V)3Si phase was precipitated in a nanocrystalline Al matrix. Scanning electron microscopy (SEM) images of the bulk samples represented a homogeneous and uniform microstructure that was superior to those previously obtained by rapid solidification-powder metallurgy (RS-PM). Nanostructured Al-8.5Fe-1.3V-1.7Si and Al-11.6Fe-1.3V-2.3Si alloys exhibited high HV hardness values of ∼205 and ∼254, respectively, which are significantly higher than those reported for the RS-PM counterparts.

Mechanical Properties and Thermal Stability of Nanostructured Al/Al12(Fe,V)3Si Alloys Produced by Powder Metallurgy

The present paper deals with the properties of bulk nanostructured Al-Fe-V-Si alloys containing 16, 27, and 37 vol.% of Al12(Fe,V)3Si precipitates. The elemental powders were subjected to high-energy ball milling for 60 h followed by hot-pressing in a uniaxial die at 550 °C under 300 MPa. Mechanical properties of consolidated samples were evaluated by hardness, room temperature, and high temperature compression tests and compared with those of rapid solidification-powder metallurgy (RS-PM) counterparts and also those available for conventional and high temperature Al alloys. The results showed that the nanostructured alloy containing Al12(Fe,V)3Si precipitates has good thermal stability at high temperatures. Room temperature compression tests demonstrated that the strength increases and the ductility decreases with increasing the volume percentage of Al12(Fe,V)3Si precipitates. The room temperature yield strength of nanostructured alloys was in the range of 560-758 MPa depending on Al12(Fe,V)3Si content. These values are much higher than those for RS-PM counterparts. In addition, nanostructured Al-Al12(Fe,V)3Si alloys exhibited better strength at elevated temperatures compared with other Al alloys.

Microstructure and mechanical properties of rapidly solidified/powder metallurgy Mg–6Zn and Mg–6Zn–5Ca at room and elevated temperatures

Rapid solidification/powder metallurgy (RS/PM) Mg–6Zn and Mg–6Zn–5Ca (wt.%) alloys in form of rods were prepared by hot extrusion with RS powders, produced via atomization of the alloy melt and subsequent splat-quenching between a couple of water-cooled copper rolls. The microstructure and mechanical properties of the alloys at both room and elevated temperatures were investigated. The results showed that with an addition of 5wt.%Ca to the Mg–6Zn alloy, the microstructure of the alloy was refined significantly, in which the grain size ranged from 500nm to 1μm and the number of finely dispersed particles increased substantially. This resulted in an increase in the compressive strength of alloy up to 408MPa at room temperature. Although the strength of both the alloys decreased with an increase in test temperature, the Mg–6Zn–5Ca alloy exhibited a high strength of 202MPa at 200°C, which resulted mainly from the formation of particles of the stable intermetallic phase Ca2Mg6Zn3, which were effective in pinning dislocations and grain boundaries at elevated temperatures. In addition, the formation of deformation twins and their intersections, and the interaction between the twins and the Ca2Mg6Zn3 particles during compressive deformation at 200°C contributed to the strengthening of the alloy. However, the Mg–6Zn alloy exhibited a very low strength of 41MPa at 200°C, which resulted from dynamic recrystallization softening.

Application of rapid solidification powder metallurgy processing to prepare Cu–Al–Ni high temperature shape memory alloy strips with high strength and high ductility

Cu–Al–Ni high temperature shape memory alloy (HTSMA) strips were successfully prepared from rapid solidified water atomized Cu–Al–Ni pre-alloyed powders via hot densification rolling of unsheathed sintered powder preforms. Finished heat-treated Cu–Al–Ni alloy strips had fine-grained structure, average grain size approximately 16μm, and exhibited a combination of high strength and high ductility. It has been demonstrated that the redistribution of nano-sized alumina particles, present on the surface as well as inside the starting water atomized Cu–Al–Ni pre-alloyed powder particles, due to plastic deformation of starting powder particles during hot densification rolling resulted in the fine grained microstructure in the finished SMA strips. The finished SMA strips were almost fully martensitic in nature, consisting of a mixture of β1′ and γ1′ martensite. The average fracture strength and fracture strain of the finished SMA strips were 810MPa and 12%, respectively, and the fractured specimens exhibited primarily micro-void coalescence type ductile nature of fracture. Finished Cu–Al–Ni SMA strips exhibited high characteristic transformation temperatures and an almost 100% one-way shape recovery was obtained in the specimens up to 4% applied deformation pre-strain. The retained two-way shape memory recovery increased with increasing applied training pre-strain, achieving a maximum value of 16.25% at 5% applied training pre-strain.

MICROSTRUCTURE STUDY OF A RAPID SOLIDIFICATION POWDER METALLURGY HIGH TEMPERATURE TITANIUM ALLOY

The high temperature titanium alloy with rare earth element Nd addition was prepared by rapidly solidified powder metallurgy(RS-PM) processing.The microstructure of RS-PM high temperature titanium alloy has been investigated systemically.Microstructure study showed that theα' martensite phase in the RS powders initially decomposed at 700℃and vastly at 900℃during the hot isostatic pressing(HIP) process.The decomposition products were equiaxed or lamellarαphase as well as grain boundaryβphase.The microstructure of the specimen HIPed at the temperature in(α+β) phase field contained equiaxedαphase,lamellarαphase andβphase.The size of equiaxedαphase increased while the aspect ratio of the lamellarαphase decreased when the HIP temperature increased.The microstructure of the specimen HIPed at the temperature inβphase field contained coarsed lamellarαphase,grain boundaryαphase andβphase.The microstructure became finer with decreasing the powder particle size.The microstructure of the sample HIPed in the(a+β) phase field and then heat treated in the(a+β) phase field was bi-modal microstructure containing equiaxedαphase andβtransformed structure.The microstructure of the sample HIPed in theβphase field and then heat treated in the(a+β) phase field was ternary microstructure containing equiaxedαphase,lamellarαphase andβtransformed structure.The microstructure of the sample HIPed in the {a+β) phase field orβphase field and then heat treated in theβphase field was basket-weave structure.The proportion of rich-Nd phases increased with increasing the Nd content,resulting in the reduction of originalβgrain size.

Oxidation and Creep Limited Lifetime of Kanthal APMT®, a Dispersion Strengthened FeCrAlMo Alloy Designed for Strength and Oxidation Resistance at High Temperatures

Kanthal APMT® is an FeCrAlMo alloy optimized for continuous service up to 1,250 °C (~2,300 °F). Rapid solidification powder metallurgy applied on this FeCrAlMo composition provided an oxide dispersion strengthened microstructure. The alloy exhibits an attractive combination of resistance to oxidation and corrosion and excellent form stability. In this study, oxidation and corrosion properties were investigated, as well as mechanical properties at elevated temperature. It was shown that an adherent alumina layer on the alloy surface formed during service that provided excellent resistance to corrosion attacks in most industrial atmospheres and gave great advantages compared to chromia forming high temperature Ni-base alloys in terms of maximum operating temperature and life. Focus was set on oxidation and creep properties but also other important aspects are discussed.

Improved corrosion resistance of a high-strength Mg–Al–Mn–Ca magnesium alloy made by rapid solidification powder metallurgy

Abstract The mechanical property and in particular the corrosion behavior of an Mg–Al–Mn–Ca alloy produced by spinning water atomization process (SWAP) were investigated and compared to those of the alloys made by gravity cast and hot extrusion. It is found that the SWAPed alloy has not only superior mechanical properties but also distinguished corrosion resistance. The corrosion resistance of the SWAPed alloy is about 2.5 and 10 times higher than that of the hot-extruded and as-cast alloys, respectively, when immersed in 0.1 M NaCl solution. Potentiodynamic polarization shows that both the anodic and cathodic current densities of the three alloys in 0.1 M NaCl solution are in the order of SWAPed alloy

A fundamental study of laser welding of hot extruded powder metallurgy (P/M) AZ31B magnesium alloy

Abstract Laser welding characteristics of a hot extruded AZ31B magnesium alloy produced by rapid solidification powder metallurgy (P/M) were investigated. Extremely porous weld metals were formed under all the employed welding conditions although the base material possessed a fully dense microstructure without pores. Features of porosity morphology in the weld metals as well as X-ray transmission real-time observation results of the molten pool during welding implied that pores originated from the base material. Investigation of the chemical compositions of the base material revealed the presence of a small amount of oxygen and nitrogen. However, the high pressure applied in the initial production processes of the base material caused these gases to expand to large volumes once released when the material was melted during welding, resulting in the formation of large pores. The use of insert-layer of conventionally extruded AZ31B alloy did not improve the situation because a large amount of porosity was formed even when melting of the P/M alloy was minimized.

The texture and anisotropy of hot extruded magnesium alloys fabricated via rapid solidification powder metallurgy

Rapid solidification magnesium alloy powders produced by spinning water atomization process were hot extruded into rectangular bars, from which tensile and compression samples have been cut at 0°, 45° and 90° angles from the extrusion direction to study their anisotropy. Electron back-scattered diffraction analysis has been used to investigate the texture evolution during the extrusion process. Texture parameters like the Schmid factor and the intensity of (0 0 0 1) basal plane in the pole figure have been evaluated and correlated to the mechanical properties. Results have shown that the extruded rods exhibited high strength and relatively less anisotropy compared to other previously reported values for wrought magnesium alloys. Tensile and compression yield stresses have shown very similar values to each other at all loading directions. This limited anisotropy could be linked to both the fine grained and inter-metallic-compound-dispersed microstructure of the extruded alloys. Dynamic recrystallization behavior during hot extrusion has also been investigated in the present study.

Application of rapid solidification powder metallurgy to the fabrication of high-strength, high-ductility Mg–Al–Zn–Ca–La alloy through hot extrusion

The microstructure and mechanical properties of hot extruded Mg–7Al–1Zn–1Ca powder alloys with an addition of 1.5% La or 3.3% La were investigated. Both rapidly solidified powders, produced via spinning water atomization process, and cast billets were extruded at 573, 623 and 673 K to optimize the processing conditions for obtaining better mechanical response. Powders were consolidated using both cold compaction and spark plasma sintering. The tensile properties of the extruded alloys were then evaluated and correlated to their microstructures. The results showed that the use of rapidly solidified Mg–7Al–1Zn–1Ca alloy powders with La additions could lead to effective grain refinement and super saturation of alloying elements, which in turn resulted in the improved mechanical response. The Mg–7Al–1Zn–1Ca–1.5La alloy extruded at 573 K attained ultimate tensile strength of 450 ± xx MPa and elongation of 17 ± xx%, superior to the Mg–7Al–1Zn–1Ca–3.3La alloy and other Mg alloys like Mg–Al–Mn–Ca. This may help extend the application of Mg alloys to higher load-carrying parts while maintaining the excellent advantage of light weight.

Structure and mechanical properties of an AlCr6Fe2Ti1 alloy produced by rapid solidification powder metallurgy method

Abstract In the present paper, the structure and properties of a Al–Cr–Fe–Ti alloy produced by powder metallurgy are described. An initial rapidly solidified powder alloy was prepared by the pressure nitrogen melt atomisation. Subsequently, the granulometric powder fraction of less than 45 μm was hot-extruded. According to X-ray diffraction and transmission electron microscopy observation, the compact material is composed of α-Al grains and spheroids of intermetallic phases. The α-Al grains of the compacted material are recrystallized and neither residual stress nor texture were observed. The values of ultimate tensile strength and yield strength of the investigated material were similar to the values for conventional Al-based alloys. Dependences of ultimate tensile strength and yield strength on temperature were also measured. Excellent thermal stability of the powder metallurgy produced Al–Cr-based material was proven by room-temperature hardness measurement after long-term annealing at elevated temperature.

Microstructure and Tensile Properties of ZK60 Alloy Fabricated by Simplified Rapid Solidification Powder Metallurgy (S-RS P/M) Process

This study investigated the microstructures and mechanical properties of ZK60 alloy prepared by a simplified rapid solidification powder metallurgy (RS P/M) processing system (S-RS P/M), which consists of warm press in dry air and hot extrusion. Microstructure characterizations showed that S-RS P/M alloy consisted of magnesium matrix and oxide stringers of ∼1 μm in width. TEM (transmission electron microscopy) observations illustrated nano-size magnesia particles (10–30 nm) constituted oxide stringer in detail. Due to a relatively higher volume of nano-size magnesia particle produced during S-RS P/M process, 0.2% yield strength of S-RS P/M ZK60 alloy was found to be as high as 382 MPa, which is 10% higher than that of RS P/M alloy. The improvement in mechanical properties is mainly attributed to the combination effects of Orowan mechanism and coefficient of thermal expansion (CTE) mismatch because of the approximately same average grain size.

Microstructure and mechanical properties of hot extruded Mg–Al–Mn–Ca alloy produced by rapid solidification powder metallurgy

The microstructure and mechanical properties of hot extruded Mg–Al–Mn–Ca alloy was investigated. Both rapid solidified powders and cast billets were extruded at 573, 623 and 673 K to optimize the processing conditions for obtaining better mechanical response. Powder was consolidated to prepare the extrusion billets using both cold compaction and Spark Plasma Sintering at 473 K. The tensile properties of the extruded alloy were then evaluated and correlated to the observed microstructure. The results show that the use of rapid solidified powder could lead to effective grain refinement, which in turn resulted in the improved mechanical response, especially compared to the extruded conventional cast material.

Effect of multiple additives (Mn and Zr) on microstructure of P/M 7000 series aluminum alloys

Mesoalite series alloys were formed using rapid solidification powder metallurgy (RS-P/M) by hot extrusion. The addition of Mn and Zr to the basic Mesoalite alloy (Meso10) in excess led to continuous dynamic recrystallization (DRX) in the alloy during hot extrusion through a different mechanism. In order to achieve a synergistic effect, Mn and Zr additives were used simultaneously. It was found that the DRX mechanism was governed by the addition of Mn, while the Zr addition was effective in coarsening control.

Effect of Mn Intermetallic Particle on Microstructure Development of P/M Al-Zn-Mg-Cu-Mn Alloy

The Mesoalite alloy is formed using rapidly solidified powder metallurgy (RS-P/M) by hot extruding the RS powder produced by the atomization method. Meso20 is a Mesoalite alloy with a chemical composition of Al-9.5Zn3Mg-1.5Cu-4Mn-0.04Ag (mass%). Meso20 contains fine grains and precipitated intermetallic Mn compounds, and has a tensile strength of 910 MPa. During hot extrusion, dynamic recrystallization occurs and the fine grains develop. During heat treatment of Meso20, rod-like and granular Mn intermetallic compounds precipitate. The rod-like compounds are about 1 Ìm in length and the granular compounds are about 1 Ìm in diameter. X-ray diffraction measurement, transmission electron microscopy and energy dispersive X-ray (TEM/EDX) analysis and Rietveld analysis revealed the chemical composition of the granular and rod-like Mn intermetallic precipitates to be 86.5Al-10.9Mn-0.4Cu-0.9Zn-1.3Mg and 80.5Al - 10.3Mn-4.2Cu-2.5Zn-2.5Mg (mass%), respectively. The granular and rod-like compounds were identified as the Al6Mn and Q phases, respectively, with both belonging to the space group Cmcm. The lattice constants of Al6Mn were a=0.754 nm, b=0.648 nm c=0.855 nm and those of the Q phase were a=0.765 nm b=2.34 nm c=1.25 nm. Meso10, with a chemical composition of Al-9.5Zn-3Mg-1.5Cu-0.04Ag (mass%), contains no Mn and does not have fine grains, but rather coarse fibrous grains elongated along the extrusion direction. Thus the Mn intermetallic precipitates in Meso20 clearly affect the formation of fine grains. Microstructure development was studied during hot extrusion by observation using high resolution Electron Back Scattering Pattern method. Fine grains were found to develop in areas, which were relatively abundant in granular Mn intermetallic precipitates.

분무 주조 과공정 Al-Si 계 합금의 응력이완 및 Creep 천이 거동

Hypereutectic Al-Si alloys have been regarded attractive for automotive and aerospace application, due to high specific strength, good wear resistance, high thermal stability, low thermal expansion coefficient and good creep resistance. Spray casting of hypereutectic Al-Si alloy has been reported to provide distinct advantages over ingot metallurgy (IM) or rapid solidification/powder metallurgy (RS/PM) process in terms of microstructure refinement. In this study, hypereutectic Al-25Si-2.0Cu-1.0Mg alloy was prepared by OSPREY spray casting process. The change of strain rate sensitivity and Creep transition were analyzed by using the load relaxation test and constant creep test. High temperature deformation behavior of the hypereutectic Al-Si alloy has been investigated by applying the internal variable theory proposed by Chang et al. Especially, the creep resistance of spray casted hypereutectic Al-Si alloy can be enhanced considerably by the accumulation of prestrain.

Development of Constitutive Equation on Superplastic RS P/M Mg–Y–Zn Alloy

A constitutive equation of rapid solidification (RS) powder metallurgy (P/M) magnesium alloy was constructed analytically from normalized strain rate-stress plots. Data related to RS P/M magnesium alloy showed deviation from those of conventional superplastic magnesium alloys; they indicated greater strength or lower strain rates than conventional superplastic magnesium alloys because the grains have a unique structure on superplastic flow. A constitutive equation for superplastic flow was developed using a metal matrix composite model.