Application of pre-alloyed powders for diamond tools by ultrahigh pressure water atomization

Copper, iron and cobalt based pre-alloyed powders for diamond tools were prepared by ultrahigh pressure water atomization（UPWA） process. Pre-alloyed powders prepared by different processes including UPWA, conventional water atomization （CWA） and elemental metal mechanical mixing （EMMM） were sintered to segments and then compared in mechanical properties, holding force between matrix and diamond, fracture morphology of blank and sintering diamond section containing matrix. The results showed that the pre-alloyed powder prepared by UPWA exhibits the best mechanical properties including the relative density, the hardness and the bending strength of matrix sinteredsegment. Sintered segments fractography of UPWA pre-alloyed powder indicatesmechanical mosaic strength and chemical bonding force between the pre-alloyed powder and the diamond, leading to the great increase in the holding force between matrix and diamond. The mechanical performance andthe service life of diamond tools were greatly improved by UPWA pre-alloyed powders.

Comparison of Cu−Al−Ni−Mn−Zr shape memory alloy prepared by selective laser melting and conventional powder metallurgy

This work aimed to investigate and critically analyze the differences in microstructural features and thermal stability of Cu−11.3Al−3.2Ni−3.0Mn−0.5Zr shape memory alloy processed by selective laser melting(SLM)and conventional powder metallurgy.PM specimens were produced by sintering 106−180μm pre-alloyed powders under an argon atmosphere at 1060°C without secondary operations.SLM specimens were consolidated through melting 32−106μm pre-alloyed powders on a Cu−10Sn substrate.Mechanical properties were measured through Vickers hardness testing.Differential scanning calorimetry was conducted to assess the martensitic transformation temperatures.X-ray diffraction patterns were collected to identify the metallurgical phases.Optical and scanning electron microscopy was used to analyze the microstructural features.b′1 martensite was found,irrespective of the processing route,although coarser martensitic variants were present in PM-specimens.In conventional powder metallurgy samples,intergranular eutectoid constituents and stabilized austenite also formed at room temperature.PM-specimens showed similar average hardness values to the SLM-specimens,albeit with high standard deviation linked to the porosity.The specimens processed by SLM showed reversible martensitic transformation(T0=171°C).PM-processed specimens did not show shape memory effects.

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 cerium on wettability of mechanically milled Cu-based brazing alloy powder

CuSn powders and Till2 powders were milled using high energy mechanical milling to prepare Cu-based alloy powders for brazing diamond. And Ce was added to the milled Cu-based alloy powders to improve the wettability. It is found that the wetting angle reaches the minimum value 13.2° and the maximum spreading area 178 mm2 is achieved when the amount of Ce is 0.75 wt%. And Ce remarkably reduces the surface tension of liquid alloy, which improves the climbing height along the diamond and forms a massive support profile. And the results show that Ce can effectively improve the transverse rupture strength （TRS） due to high wettability. The wear characteristics of the diamonds brazed with Cu-based alloy containing 0.75 wt% Ce mainly consist of integrity, micro-fracture, fracture and rubdown, diamonds pull-out can not easily happen.

Process-microstructure-properties of CuAlNi shape memory alloys fabricated by laser powder bed fusion

Cu-based shape memory alloys(SMAs)show great potential in the application of high temperature,but their performance improvement combining with additive manufacturing is still challenging.In this paper,nearly defect-free(99.7%relative density)CuAlNi SMAs with two types of thermal-induced martensites,18R and 2H,were successfully fabricated by laser powder bed fusion(LPBF).The remelting printing strat-egy with systematic optimization framework including densification and printability analysis was used to get optimal process window.The twin-related self-accommodation structure with long period stacking order substructure was formed during additive manufacturing process.The as-build samples show excel-lent mechanical properties(ultimate compressive strength of 1593±10 MPa and large fracture strain of 23.0%±0.1%)with double-yielding,and outstanding shape memory effect,with maximum recoverable strain of 3.39% and nearly 100%recovery rate under compressive strain not exceeding 6%.Furthermore,the microstructural evolution in LPBF involving remelting,martensitic transformation,and 2H marten-site was discussed.This result not only builds the microstructure framework involving high reflectivity alloys and martensitic transformation but also provides insight into the applicability of LPBF process in producing Cu-based SMAs.

Tensile properties and deformation behavior of an extra-low interstitial fine-grained powder metallurgy near alpha titanium alloy by recycling coarse pre-alloyed powder

An extra-low interstitial near alpha alloy Ti-3Al-2Zr-2Mo(wt%) was fabricated by hydrogenation and thermomechanical consolidation(TMC) of the coarse and spherical pre-alloyed powder with particle sizes of 60 to 270 μm. The coarse powder is a byproduct of pre-alloyed powder produced for selective laser and electron beam additive manufacturing. The TMC process involves powder compaction, fast sintering,in-situ dehydrogenation and an immediate hot extrusion to form a fully dense and fine-grained martensitic microstructure. Further dehydrogenation in vaccum at 700 °C converted the martensitic microstructure into an interwoven α/β microstructure which exhibited an improved yield strength, apparent necking and premature cracking at grain boundary α(α_(GB)) ribbons. A further annealing of 880 ℃/1 h/AC led to the formation of a fine-grained α/β_(t)composite structure, which achieved an enhance ultimate tensile strength of 835 MPa and excellent tensile ductility of 16.0%. Analysis of the deformation behavior of the alloy in different states revealed that the α/β_(t)composite structures brought about an enhanced strain hardening capability by heterogeneous deformation effect of hard β_(t)and soft α-laths, which inhibited the formation of microcracks and consequently improved the coordinated deformation.

Deformation mechanism of Cu-Al-Ni shape memory alloys fabricated via laser powder b e d fusion:Tension-compression asymmetry

Introducing the unique advantage of additive manufacturing technology into copper-based shape memory alloys(SMAs)to fabricate high-performance alloys has garnered great attention in recent years,but the intrinsic relationships between microstructure and mechanical properties need to be further clarified.In this paper,the microstructural evolution of ternary CuAlNi SMAs fabricated by laser powder bed fusion(LPBF)under the tensile-compressive loading was investigated to determine the underlying mechanism of tension-compression asymmetry,that is,excellent compressive but poor tensile properties.Multiscale characterization of the different deformation stages revealed the numerous activated deformation mech-anism on the 18R martensite matrix.A twin-related transformation dominated the main plastic defor-mation process due to lower stacking faults energy and high-density pre-existing planer defects in the CuAlNi SMAs.Deformation twinning nucleated at prior austenite boundaries and developed into parallel and network structures inside the parent grain of different sizes.In addition,the preferred orientation in different stages,the stress-inducedγphase transformation,and the interaction between dislocations and stacking faults are discussed.These results not only provide significant insights to understand the detwinning and deformation twinning process of SMAs but also establish the essential framework of mi-crostructure and mechanical properties of Cu-based SMAs fabricated by LPBF.

Microstructure Design and Heat Response of Powder Metallurgy Ti_2AlNb Alloys

Pre-alloyed powder of Ti-22Al-24Nb-0.5Mo（atomic fraction,%） was prepared by gas atomization.Powder metallurgy（PM） Ti 2AlNb alloys were prepared by a hot isostatic pressing（HIPing） route.The influence of experimental variables including HIPing temperatures,solution and aging temperatures on microstructure and properties of PM Ti 2AlNb alloys was studied.The results showed that HIPing temperature affected the porosity distribution and mechanical properties of PM Ti 2AlNb alloys.The microstructure and mechanical properties of the PM Ti 2AlNb alloys changed obviously after various post heat treatments,and a good combination of tensile strength,ductility and rupture lifetime was obtained through an optimized heat treatment in the present work.