Integrated high-performance and accurate shaping technology of low-cost powder metallurgy titanium alloys: A comprehensive review

The practical engineering applications of powder metallurgy (PM) Ti alloys produced through cold compaction and pressure-less sintering are impeded by poor sintering densification, embrittlement caused by excessive O impurities, and severe sintering deforma-tion resulting from the use of heterogeneous powder mixtures. This review presents a summary of our previous work on addressing the above challenges. Initially, we proposed a novel strategy using reaction-induced liquid phases to enhance sintering densification. Near- complete density (relative density exceeding 99%) was achieved by applying the above strategy and newly developed sintering aids. By focusing on the O-induced embrittlement issue, we determined the onset dissolution temperature of oxide films in the Ti matrix. On the basis of this finding, we established a design criterion for effective O scavengers that require reaction with oxide films before their dissol-ution. Consequently, a ductile PM Ti alloy was successfully obtained by introducing 0.3wt% NdB6 as the O scavenger. Lastly, a powder- coating strategy was adopted to address the sintering deformation issue. The ultrafine size and shell-like distribution characteristics of coating particles ensured rapid dissolution and homogeneity in the Ti matrix, thereby facilitating linear shrinkage during sintering. As a result, geometrically complex Ti alloy parts with high dimensional accuracy were fabricated by using the coated powder. Our fundament-al findings and related technical achievements enabled the development of an integrated production technology for the high-performance and accurate shaping of low-cost PM Ti alloys. Additionally, the primary engineering applications and progress in the industrialization practice of our developed technology are introduced in this review.

Ceramic particles reinforced copper matrix composites manufactured by advanced powder metallurgy:preparation, performance, and mechanisms

Copper matrix composites doped with ceramic particles are known to effectively enhance the mechanical properties,thermal expansion behavior and high-temperature stability of copper while maintaining high thermal and electrical conductivity.This greatly expands the applications of copper as a functional material in thermal and conductive components,including electronic packaging materials and heat sinks,brushes,integrated circuit lead frames.So far,endeavors have been focusing on how to choose suitable ceramic components and fully exert strengthening effect of ceramic particles in the copper matrix.This article reviews and analyzes the effects of preparation techniques and the characteristics of ceramic particles,including ceramic particle content,size,morphology and interfacial bonding,on the diathermancy,electrical conductivity and mechanical behavior of copper matrix composites.The corresponding models and influencing mechanisms are also elaborated in depth.This review contributes to a deep understanding of the strengthening mechanisms and microstructural regulation of ceramic particle reinforced copper matrix composites.By more precise design and manipulation of composite microstructure,the comprehensive properties could be further improved to meet the growing demands of copper matrix composites in a wide range of application fields.

Thermal stability and microstructure development of cast and powder metallurgy produced Mg-Y-Zn alloy during heat treatment

Response to isochronal annealing up to 440 ℃ of squeeze cast Mg–Y–Zn alloy and of the same alloy prepared by powder metallurgy(PM)and extruded at 280 ℃ was studied by resistivity and microhardness measurement,differential scanning calorimetry(DSC)and microstructure investigation.Electrical resistivity was measured at 77 K and microhardness was measured at room temperature after each annealing step.DSC measurement was performed at various heating rates.Transmission and scanning electron microscopy and optical microscopy revealed ribbons of long-period ordered structure(LPSO)18R and planar defects within grain boundaries.Relatively high density of planar defects was found in grain interiors of the cast alloy with the grain size approximately 50μm.Well pronounced subgrains were observed in the PM prepared alloy.Secondary phase particles decorate grain boundaries in this alloy.Three precipitation processes were detected in the cast alloy during repeated isochronal annealing up to 440 ℃,whereas only one significant process was revealed in the PM alloy.These processes were identified as embedding of stacking faults by solutes,development and rearrangement(18R→14H)of LPSO phase and development of grain boundary particles.A coarsening of grain boundary particles rich in Y and Zn only proceeds in the PM alloy.Activation energies of the precipitation processes were determined.Microhardness exhibits good thermal stability against annealing up to 360 ℃ in the PM alloy.

Development of Mg based biomaterial with improved mechanical and degradation properties using powder metallurgy

In the present work,biocompatible materials such as niobium(Nb),zinc(Zn)and calcium(Ca)have been blended with magnesium(Mg)to develop a novel biomaterial(BM)with improved mechanical and corrosion resistant properties.Powder metallurgy(PM)technique was used to fabricate Mg based BM.The powder of all aforementioned materials were mixed homogenously in specific quantities to create a uniform composite component.In order to analyse the influence of process parameters on the mechanical properties of the fabricated part,experiments were performed considering central composite design(CCD).The effect of powder metallurgical parameters namely percentage Nb,compaction pressure,heating rate,sintering temperature and soaking time on the ultimate compressive strength(UCS)and sintered density was studied in the present study.It was found that the UCS and sintered density increased with increase in compaction pressure,heating rate and sintering temperature.The results also revealed that the increase in soaking time and percentage Nb,increased sintered density and UCS to a certain limit.Subsequent increase in these two parameters,sintered density and UCS decreased.Scanning electron microscopy(SEM)images of the fabricated samples showed reduction in porosity with the increase in heating rate.Moreover,X-ray diffraction(XRD)results revealed that no other phase or impurities were found during sintering of Mg based BMs.The optimum process parameters were obtained to develop Mg based BM for maximum UCS and sintered density.Furthermore,the Mg based BM samples fabricated at optimum process parameters were used for corrosion testing in simulated body fluid(SBF)solution at a temperature of 37±0.5℃.The Mg based BM yielded improved mechanical properties with reduced corrosion rates as compared to pure Mg.

Development of Cu-Exfoliated Graphite Nanoplatelets (xGnP) Metal Matrix Composite by Powder Metallurgy Route

In the present investigation the possibility of using exfoliated graphite nanoplatelets (xGnP) as reinforcement in order to enhance the mechanical properties of Cu-based metal matrix composites is explored. Cu-based metal matrix composites reinforced with different amounts of xGnP were fabricated by powder metallurgy route. The microstructure, sliding wear behaviour and mechanical properties of the Cu-xGnP composites were investigated. xGnP has been synthesized from the graphite intercalation compounds (GIC) through rapid evaporation of the intercalant at an elevated temperature. The thermally exfoliated graphite was later sonicated for a period of 5 h in acetone in order to achieve further exfoliation. The xGnP synthesized was characterized using SEM, HRTEM, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. The Cu and xGnP powder mixtures were consolidated under a load of 565 MPa followed by sintering at 850°C for 2 h in inert atmosphere. Cu-1, 2, 3 and 5 wt% xGnP composites were developed. Results of the wear test show that there is a significant improvement in the wear resistance of the composites up to addition of 2 wt% of xGnP. Hardness, tensile strength and strain at failure of the various Cu-xGnP composites also show improvement upto the addition of 2 wt% xGnP beyond which there is a decrease in these properties. The density of the composites decreases with the addition of higher wt% of xGnP although addition of higher wt% of xGnP leads to higher sinterability and densification of the composites, resulting in higher relative density values. The nature of fracture in the pure Cu as well as the various Cu-xGnP composites was found to be ductile. Nanoplatelets of graphite were found firmly embedded in the Cu matrix in case of Cu-xGnP composites containing low wt% of xGnP.

Effect of Die Wall Lubrication on Warm Compaction Powder Metallurgy

Die wall lubrication was applied on warm compaction powder metallurgy in hope to reduce the concentration level of the admixed lubricant since lubricant is harmful to the mechanical property of the sintered materials. Iron-based samples were prepared by die wall lubricated warm compaction at 135 ℃ and 175 ℃, using polytetrafluoroethylene (PTFE) emulsion as die wall lubricant. A compacting pressure of 700 MPa and 550 MPa were used. The admixed lubricant concentration ranging from 0 to 0.6 wt.% was used in this study. Compared with non-die wall lubricated samples, the die wall lubricated samples have higher green densities. Results show that in addition to the decrease in ejection forces, green density of the compacts increased linearly with the decrease in admixed lubricant content. Mechanical property of the sintered compacts increase sharply when the admixed lubricant concentration reduced to 0.125 wt.% or less. Ejection force data indicated that samples with die wall lubrication show lower ejection forces when compared with samples without die wall lubrication. No scoring was observed in all experiments even for samples contain no admixed lubricant. Our results indicated that under experimental condition used in this study, no matter at which compaction pressure, compaction temperature, graphite and lubricant contents in the powder the die wall lubricated warm compaction would give the highest green density and lowest ejection force. It can be concluded that combination of die wall lubrication and warm compaction can provide P/M products with higher density and better quality. It is a feasible way to produce high performance P/M parts if suitable die wall lubrication system was applied.

Assessment of the SiC＿p Distribution Uniformity in SiC＿p／Al Composites Made by Powder Metallurgy

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SYNTHESIS OF Ti-47Al-2Cr-2Nb ALLOY THROUGH ELEMENTAL POWDER METALLURGY

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A homogenous microstructural Mg-based matrix model for orthopedic application with generating uniform and smooth corrosion product layer in Ringer’s solution:Study on biodegradable behavior of Mg-Zn alloys prepared by powder metallurgy as a case

For high corrosion resistance and extensively modified biodegradable Mg-based alloys and composites for bone implants,a new Mgbased matrix model prepared by powder metallurgy is discussed and developed.In this research,Mg-5 wt.%Zn alloys were selected as a case.And they were impacted by hot extrusion and aging treatments to construct microstructure with different characteristics.Their selfforming corrosion product layer in Ringer’s solution,biodegradable behavior and corrosion mechanism were minutely investigated by in vitro degradation,electrochemical corrosion and cytocompatibility.The results demonstrated the extruded Mg-5 wt.%Zn alloy aged for 96 h showed high corrosion resistance,good biocompatibility for L929 and excellent ability of maintaining sample integrity during the immersion.Significantly,the alloy showed fine-grain microstructure and uniform distributed hundred nano-sized second phases,which promoted the formation of the uniform and smooth corrosion product layer at the beginning of immersion.The corrosion product layer was more stable in chloride containing aqueous solution and could be directly formed and repaired quickly,which effectively protected the matrix from further corrosion.In addition,an ideal model of Mg-based matrix for bone tissue engineering was tried to presume and propose by discussing the causal relationship between microstructure and bio-corrosion process.

Fabrication and characterization copper/diamond composites for heat sink application using powder metallurgy

Copper composites reinforced with diamond particles were fabricated by the powder metallurgical technique. Copper matrix and diamond powders were mixed mechanically, cold com- pacted at 100 bar then sintered at 900?C. The prepared powders and sintered copper/diamond composites were investigated using X-ray diffraction (XRD) and scanning electron microscope equipped with an energy dispersive X-ray analysis (SEM/EDS). The effect of diamond contents in the Cu/diamond composite on the different properties of the composite was studied. On fracture surfaces of the Cu/uncoated diamond composites, it was found that there is a very weak bonding between diamonds and pure copper matrix. In order to improve the bonding strength between copper and the reinforcement, diamond particles were electroless coated with NiWB alloy. The results show that coated diamond particles distribute uniformly in copper composite and the interface between diamond particles and Cu matrix is clear and well bonded due to the formation of a thin layer from WB2, Ni3B, and BC2 between Cu and diamond interfaces. The properties of the composites materials using coated powder, such as hardness, transverse rupture strength, thermal conductivity, and coefficient of thermal expansion (CTE) were exhibit greater values than that of the composites using uncoated diamond powder. Additionally, the results reveals that the maximum diamond incorporation was attained at 20 Vf%. Actually, Cu/20 Vf% coated diamond com- posite yields a high thermal conductivity of 430 W/mK along with a low coefficient of thermal expansion (CTE) 6 × 10–6/K.

Fabrication and characteristics of magnesium alloys produced via powder metallurgy

Magnesium aluminum alloy materials were fabricated via powder metallurgy. Microstructural evolution, thermal stability, tensile properties and fracture mechanism of the hot extruded magnesium alloys were investigated. Microstructural observation revealed that all alloys have fine equiaxed grains due to dynamic recrystallization during hot extrusion with Mg 17 Al 12 precipitating along grain boundaries. The DSC analyses exhibited that because diffusion rate of Al into Mg is slow in solid state sintering process, Al concentration in localized region after sintering is still high enough to cause eutectic reaction. The tensile test showed that 0.2% yield strength, ultimate tensile strength and elastic modulus increase and elongation decrease with increasing Al content. Mg 9%Al obtains the best combination of mechanical properties among the investigated alloys. Fracture surface observation showed ductile fracture to be a dominant failure mode. Abundant dimples and tear ridges are found in the fracture surfaces. Grain boundary weakening results from the precipitate Mg 17 Al 12 caused intergranular cracks during tensile test. [

The Effect of Time, Percent of Copper and Nickel on the Natural Precipitation Hardness of Al – Cu – Ni Powder Metallurgy Alloys Using Design of Experiments

In this investigation, the effect of time, percentage of copper and nickel on the hardness property of aluminum based powder metallurgy alloys were studied. A full factorial analysis with four levels for each factor was used. The samples were produced using powder metallurgy process, and then subjected to natural aging where heat treatment was conducted for all samples together at 550°C for 3 hours before quenching in water. Then, the samples were left at room temperature for 936 hours (39 days) to allow traces atoms to diffuse and form coherent phases which increase the hardness. It was found that the hardness was firstly increased with time for about 300 hours after the quenching time, and then it tends to remain constant after that. However, the hardness drop at overage stage was not observed until the end of 936 hours. To get a full analysis of the natural aging we used design of experiment tool to study the effect of %Cu, %Ni and aging time on the hardness. The results showed that the hardness was influenced significantly by all considered factors and interactions between them.

Processing TiAl-Based Alloy by Elemental Powder Metallurgy

TiAl-based alloys with various compositions (including Ti-48Al, Ti-47Al-2Cr-2Nb, Ti-47Al-2Cr- 2Nb-0.2B and Ti-47Al-3Cr, in mole fraction) had been prepared by elemental powder metallurgy (EPM). The results have shown that the density of the prepared Ti-48Al alloy increases with increasing hot pressing temperature up to 1300℃. The Ti-48Al alloy microstructure mainly consisted of island-like Ti3Al phase and TiAl matrix at hot pressing temperature below 1300℃, however, coarse a2/r lamellar colonies and r grains appeared at 1400℃. It has also indicated that the additions of elemental Cr and B can refine the alloy microstructure. The main microstructural inhomogeneity in EPM TiAl-based alloys was the island-like a2 phase or the aggregate of a2/r lamellar colony, and such island-like structure will be inherited during subsequent heat treatment in (a+r) field. Only after heat treatment in a field would this structure be eliminated. The mechanical properties of EPM TiAl-based alloys with various compositions were tested, and the effect of alloy elements on the mechanical properties was closely related to that of alloy elements on the alloy microstructures. Based on the above results, TiAl-based alloy exhaust valves were fabricated by elemental powder metallurgy and diffusion joining. The automobile engine test had demonstrated that the performance of the manufactured valves was very promising for engine service.

CRITICAL ISSUES OF POWDER METALLURGY TURBINE DISKS

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Fabrication of homogeneously dispersed graphene/Al composites by solution mixing and powder metallurgy

Graphene-reinforced aluminum(Al) matrix composites were successfully prepared via solution mixing and powder metallurgy in this study. The mechanical properties of the composites were studied using microhardness and tensile tests. Compared to the pure Al alloy, the graphene/Al composites showed increased strength and hardness. A tensile strength of 255 MPa was achieved for the graphene/Al composite with only 0.3 wt% graphene, which has a 25% increase over the tensile strength of the pure Al matrix. Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to investigate the morphologies, chemical compositions, and microstructures of the graphene and the graphene/Al composites. On the basis of fractographic evidence, a relevant fracture mechanism is proposed.

CHARACTERISTICS OF FATIGUE SURFACE MICROCRACK GROWTH IN VICINAL INCLUSION FOR POWDER METALLURGY ALLOYS

Inclusion flaw is one of the worst flaws of powder metallurgy. The inclusion flaw plays an important role in the failure of high temperature turbine materials in aircraft components and automotive parts, especially fatigue failure. In this paper, an experimental investigation of fatigue microcrack propagation in the vicinal inclusion were carried out by the servo-hydraulic fatigue test system with scanning electron microscope (SEM). It has been found from the SEM images that the fatigue surface microcrack occurs in the matrix and inclusion. According to the SEM images, the characteristics of fatigue crack initiation and growth in vicinal inclusion for powder metallurgy alloys are analyzed in detail. The effect of the geometrical shape and material type of surface inclusions on the cracking is also discussed with the finite element method (FEM).

Interface Characterization of the SiCp/Al Composites Made by Powder Metallurgy

The interface of the SiCp/Al composites produced by powder metallurgy processing involving hotpressing above the matrix solidus temperature has been investigated by means of TEM. Several kinds of interfaces between the reinforcements and the matrix in the composite, including the clean interfaces, the faceted interfaces and the slight reaction intedeces, are presented. And most of interfaces belong to the slight reaction interfaces which are composed of the Al with different orientation from the Al matrix near the interface zone and particte-like substances produced by MgAl2O4 spinels and

Powder metallurgy of high-entropy alloys and related composites: A short review

High-entropy alloys(HEAs)have attracted increasing attention because of their unique properties,including high strength,hardness,chemical stability,and good wear resistance.Powder metallurgy is one of the most important methods used to fabricate HEA materials.This paper introduces the methods used to synthesize HEA powders and consolidate HEA bulk.The phase transformation,microstructural evolution,and mechanical properties of HEAs obtained by powder metallurgy are summarized.We also address HEA-related materials such as ceramic–HEA cermets and HEA-based composites fabricated by powder metallurgy.

Improvement of Ductility of Powder Metallurgy Titanium Alloys by Addition of Rare Earth Element

Ti-4.5AI-6.0Mo-1.5Fe， Ti-6AI-1Mo-1Fe 和 Ti-6AI-4V 合金被混合元素的粉末冶金学(下午) 准备微观结构和机械性质上的 Nd 的过程，和效果被扫描电子显微镜学(SEM ) 调查，传播电子显微镜学(TEM ) 和 X 光检查衍射(XRD ) 。因为液相的小数量发生在 sintering 期间， Nd 的增加由 1% 的最大的增长稍微增加了 sintered 钛合金的密度，这被发现。Nd 的增加在张力的力量的改进上显示出小效果，当延伸显著地被改进时。例如，没有 13percent 的 Nd 的增加， Ti-4.5AI-6.0Mo-1.5Fe 的延伸能在 1.2 wt % 的一个 Nd 内容从 1% 被增加。