Mechanical and corrosion properties of full liquid phase sintered WE43 magnesium alloy specimens fabricated via binder jetting additive manufacturing

This study investigates full liquid phase sintering as a process of fabrication parts from WE43(Mg-4wt.%Y-3wt.%RE-0.7wt.%Zr)alloy using binder jetting additive manufacturing(BJAM).This fabrication process is being developed for use in producing structural or biomedical devices.Specifically,this study focused on achieving a near-dense microstructure with WE43 Mg alloy while substantially reducing the duration of sintering post-processing after BJAM part rendering.The optimal process resulted in microstructure with 2.5%porosity and significantly reduced sintering time.The improved sintering can be explained by the presence of Y_(2)O_(3)and Nd_(2)O_(3)oxide layers,which form spontaneously on the surface of WE43 powder used in BJAM.These layers appear to be crucial in preventing shape distortion of the resulting samples and in enabling the development of sintering necks,particularly under sintering conditions exceeding the liquidus temperature of WE43 alloy.Sintered WE43 specimens rendered by BJAM achieved significant improvement in both corrosion resistance and mechanical properties through reduced porosity levels related to the sintering time.

Spark Plasma Sintering of Mg-based Alloys:Microstructure,Mechanical Properties,Corrosion Behavior,and Tribological Performance

Within the past ten years,spark plasma sintering(SPS)has become an increasingly popular process for Mg manufacturing.In the SPS process,interparticle diffusion of compressed particles is rapidly achieved due to the concept of Joule heating.Compared to traditional and additive manufacturing(AM)techniques,SPS gives unique control of the structural and microstructural features of Mg components.By doing so,their mechanical,tribological,and corrosion properties can be tailored.Although great advancements in this field have been made,these pieces of knowledge are scattered and have not been contextualized into a single work.The motivation of this work is to address this scientific gap and to provide a groundwork for understanding the basics of SPS manufacturing for Mg.To do so,the existing body of SPS Mg literature was first surveyed,with a focus on their structural formation and degradation mechanisms.It was found that successful Mg SPS fabrication highly depended on the processing temperature,particle size,and particle crystallinity.The addition of metal and ceramic composites also affected their microstructural features due to the Zener pinning effect.In degradative environments,their performance depends on their structural features and whether they have secondary phased composites.In industrial applications,SPS'd Mg was found to have great potential in biomedical,hydrogen storage,battery,automotive,and recycling sectors.The prospects to advance the field include using Mg as a doping agent for crystallite size refinement and using bulk metallic Mg-based glass powders for amorphous SPS components.Despite these findings,the interactions of multi-composites on the processing-structure-property relationships of SPS Mg is not well understood.In total,this work will provide a useful direction in the SPS field and serve as a milestone for future Mg-based SPS manufacturing.

Spark plasma sintering of tungsten-based WTaVCr refractory high entropy alloys for nuclear fusion applications

W-based WTaVCr refractory high entropy alloys (RHEA) may be novel and promising candidate materials for plasma facing components in the first wall and diverter in fusion reactors. This alloy has been developed by a powder metallurgy process combining mechanical alloying and spark plasma sintering (SPS). The SPSed samples contained two phases, in which the matrix is RHEA with a body-centered cubic structure, while the oxide phase was most likely Ta2VO6through a combined analysis of X-ray diffraction (XRD),energy-dispersive spectroscopy (EDS), and selected area electron diffraction (SAED). The higher oxygen affinity of Ta and V may explain the preferential formation of their oxide phases based on thermodynamic calculations. Electron backscatter diffraction (EBSD) revealed an average grain size of 6.2μm. WTaVCr RHEA showed a peak compressive strength of 2997 MPa at room temperature and much higher micro-and nano-hardness than W and other W-based RHEAs in the literature. Their high Rockwell hardness can be retained to at least 1000°C.

Microstructure and mechanical properties of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy sintered at different SPS temperatures

TiAl alloy bulk samples with the composition of Ti-45Al-5.5(Cr,Nb,B,Ta) (mole fraction, %) were prepared by high energy mechanical milling and spark plasma sintering (SPS) and then heat treatment. The microstructure and mechanical properties after heat treatment of TiAl alloy prepared by SPS at different temperatures were studied. The results showed that the morphology of high energy mechanically milled powder was irregular and the average grain size was about decades micrometers. X-ray diffraction analysis showed that the mechanically milled powder was composed of two phases of TiAl and Ti3Al. The main phase of TiAl and few phases of Ti3Al and TiB2 were observed in the SPS bulk samples of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy. For samples sintered at 900 °C and 1000 °C, the microstructure was duplex structure with some fine equiaxed gamma grains and thin needly TiB2 phases. With the SPS temperature increasing from 900 °C to 1000 °C, the micro-hardness was changed little, the compression strength increased from 1812 MPa to 2275 MPa and the compression ratio increased from 22.66% to 25.59%. The fractography results showed that the compression fracture transform of the SPS Ti-45Al-5.5(Cr,Nb,B,Ta) alloy was rgranular rupture.

Microstructure and corrosion behavior of NiTi shape memory alloys sintered in the SPS process

NiTi shape memory alloys(SMAs) was developed using the spark-plasma sintering(SPS) process with different average particle size(45 μm and 10 μm) under various temperature. The influence of particle size and temperature on the density, microstructure, and corrosion behavior of the NiTi in simulated body fluid was examined. The porosity decreased with increasing sintering temperature and decreasing particle size, which resulted in an increase in density of the alloy. Increasing the sintering temperature led to the formation of Ni-and Ti-rich intermetallic such as Ni3Ti and NiTi2. The formation of these secondary phases influenced the corrosion behavior of NiTi by changing its chemical composition. The planar structure of NiTi was transformed into a dendritic structure at 900℃, which resulted in the formation of uniform oxide and phosphate layers on the entire surface. A high corrosion potential and low corrosion current density were achieved with NiTi prepared with 10 μm particles at 900℃, which exhibited superior corrosion resistance.

Phase structure and electrochemical properties of laser sintered La_2MgNi_9 hydrogen storage electrode alloys

Phase structure and electrochemical properties of laser sintered La2MgNi9 alloys were studied. The sintered alloys contained a main phase, LaNi5, and a ternary La-Mg-Ni phase, with a PuNi3 structure and a small amount of LaMgNi4. The ternary La-Mg-Ni phase with a PuNi3 structure had the composition of La1.8Mg1.2Ni9 and La2MgNi9, for alloys laser sintered at 1000 and 1400 W, respectively. Owing to further reactions between LaNi5 and LaMgNi4, the amount of the PuNi3 phase increased for alloys sintered at 1400 W. Both alloys had good activation property （three charge/discharge cycles）. The discharge capacities of the sintered alloys were 321.8 and 344.8 mAh/g, respectively. Compared with the alloy laser sintered at 1000 W, the poor cyclic stability of the alloy sintered at 1400 W was mainly attributed to the lower corrosion resistance of the La2MgNi9 phase.

Phase component and microstructure of laser-sintered Mg-Ni alloys

The Mg-Ni hydrogen storage alloys were prepared using the laser sintering technology. The effects of laser sintering power on the phase component and the weight loss of Mg element for the Mg-Ni alloys were investigated. The samples P1, P2 and P3 consisted of five phases： Mg2Ni, MgNi2, Mg, Ni and MgO. The weight loss of Mg element remarkably increased at 1200 W. The addition of extra Mg significantly promoted the reaction between Mg and Ni. Mg2Ni, MgNi2, and a small amount of Ni and MgO phases were present in the samples PM （pestie milling） and BM （ball milling）. The sample PM has a homogeneous microstructure, and the contents of Mg2Ni and MgNi2 were approximately consistent with those of the Mg-Ni alloy under the equilibrium conditions. The maximum hydrogen storage capacity of the sample BM was 1.72 wt.% and the sample can be activated easily at 573 K （only 3 activation cycles）.

Microstructure evolution and mechanical properties of spark plasma sintered W-Ni-Mn alloy

Tungsten heavy alloys(90W-6Ni-4Mn)were prepared through spark plasma sintering(SPS)using micron-sized W,Ni,and Mn powders without ball milling as raw materials.The effects of sintering temperature on the microstructure and mechanicalproperties of the90W-6Ni-4Mn alloys were investigated.SPS technology was used to prepare90W-6Ni-4Mn alloys withrelatively high density and excellent comprehensive performance at1150-1250°C for3min.The90W-6Ni-4Mn alloys consistedof the W phase and theγ-(Ni,Mn,and W)binding phase,and the average grain size was less than10μm.The Rockwell hardness andbending strength of alloys first increased and then decreased with increasing sintering temperature.The best comprehensiveperformance was obtained at1200°C,its hardness and bending strength were HRA68.7and1162.72MPa,respectively.

Microstructure and mechanical properties of spark plasma sintered Ti–Mo alloys for dental applications

Ti-Mo alloys with various Mo contents from 6wt% to 14wt% were processed by spark plasma sintering based on elemental pow- ders. The influence of sintering temperature and Mo content on the microstructure and mechanical properties of the resulting alloys were investigated. For each Mo concentration, the optimum sintering temperature was determined, resulting in a fully dense and uniform microstructure of the alloy. The optimized sintering temperature gradually increases in the range of 1100-1300℃ with the increase in Mo content. The microstructure of the Ti-（6-12）Mo ahoy consists of acicular α phase surrounded by equiaxed grains of 13 phase, while the Ti-14Mo al- loy only contains single 13 phase. A small amount of fine α lath precipitated from 13 phase contributes to the improvement in strength and hardness of the alloys. Under the sintering condition at 1250℃, the Ti-12Mo alloy is found to possess superior mechanical properties with the Vickers hardness of Hv 472, the compressive yield strength of 2182 MPa, the compression rate of 32.7%, and the elastic modulus of 72.1 GPa. These results demonstrate that Ti-Mo alloys fabricated via spark plasma sintering are indeed a perspective candidate alloy for dental applications.

Microstructure Analysis of Microwave Sintered Ferrous PM Alloys

The properties and microstructure of microwave and conventional sintered Fe-2Cu-0.6C powder metallurgy （PM） alloys were investigated. The experimental results show that microwave sintered alloy has the better properties （sintered density 7.20 g/cm3, Rockwell hardness 75 HRB, tensile strength 413.90 MPa and elongation 6.0%）, compared with the conventional sintered counterpart. Detailed analyses by using optical microscopy and scanning electron microscopy （SEM） reveal that microwave sintered sample has finer microstructure with small, rounded and uniformly distributed pores, and also demonstrate the presence of more flaky and granular pearlite in the mi- crowave sintered body, both of which account for the property improvement. SEM images on the fracture morphology indicate that a mixed mode containing ductile and brittle fracture is presented in microwave sintered alloy, in contrast with the brittle fracture in conventional sintered counterpart.

Effect of Cu Addition on W-Ni-Fe Alloys Sintered at a Low Temperature

In this study, Cu was added as the third additive to lower the sintering temperature of W-Ni-Fe alloy. By adding 2 wt pct Cu, a dense 93W-3.5Ni-l.5Fe-2.0Cu tungsten alloy was obtained by hot-pressing at a low temperature of 1573 K which is a process of liquid-phase sintering. As a result, the morphology of W-Ni-Fe alloy changed obviously after the addition of Cu and the alloy had-higher relative density and rupture strength. The mechanism of the densification of W-Ni-Fe-Cu alloy at the low temperature.was then mainly investigated. It was found that, part sintering activators Ni and Fe could exist in liquid form at 1573 K due to the addition of Cu, which made it easy for Ni and Fe to dissolve W and thus the full densification of W-Ni-Fe-Cu alloy at the low temperature was realized.

Consolidation and Microstructures of Microwave Sintered W-25Cu Alloys with Fe Addition

W-25Cu alloys were microwave sintered in a 2.45 GHz multimode applicator.The densification,microstructure and their dependence on sintering mode and Fe addition were investigated in detail.Owing to the volumetric heating intrinsic in microwave processing,a microstructure with larger W grain size in center regions was observed as against larger grain size in edge regions for conventional sintering.Microwave sintering demonstrates its intrinsic advantages such as rapid heating rate,densification enhancement and microstructural homogeneity;but it undesirably promotes W grain growth.Under microwave sintering,the role of Fe addition on compact consolidation is not so substantial as under conventional sintering.Moreover Fe degrades the microstructural quality,generating worse uniformity and coarser W grains.

THE RELATION BETWEEN THE TEMPERING EFFECTS AND THE INTRINSIC COERCIVITY OF SINTERED SmCo5 ALLOY AT 750℃

The relation between the tempering effects of sinterd SmCo^(5)alloy at 750℃and its intrinsic coercivity(i^(Hc))has been studied by the use of photoelectron energy spectrum.X-ray diffraction and high-voltage electron microscope.The result is that the cause of iHc dropping seriously for sintered SmCo_(5)alloy tempered at 750 t is not the eutectoid decomposition of SmCo_(5)and the increase of oxygen.In fact,iHcdropping is caused by that some defect-rich regions in Sm_(2)Co_(17)decomposed form SmC0_(5)from nucleation centers in reversed magnetization course.

Variation in pore distribution along sample length in sintered 7xxx aluminum alloy

An experimental and computational fluid dynamics (CFD) numerical study of the sintering of an Al?7Zn?2.5Mg?1Cu alloy in flowing nitrogen was presented. Three rectangular bars with dimensions of 56 mm × 10 mm × 4.5 mm each, equally spaced 2 or 10 mm apart, were sintered in one batch at 620 °C for 40 min in a tube furnace. The pore distribution in the selected cross section of sintered samples was found to be dependent on the sample separation distance and the distance from the cross section examined to the sample end. A three-dimensional (3D) CFD model was developed to investigate the nitrogen gas behavior near each sintering surface of the three samples during isothermal sintering. The variation in porosity in the cross section of each sintered sample along sample length was found to be closely related to the nitrogen gas flow field near the sintering surfaces.

Microstructure and properties of liquid-phase sintered tungsten heavy alloys by using ultra-fine tungsten powders

The microstructure and properties of liquid-phase sintered 93W-4.9Ni-2.1Fe tungsten heavy alloys using ultra-fine tungsten powders (medium particle size of 700 nm) and original tungsten powders (medium particle size of 3 μm) were investigated respectively. Commercial tungsten powders (original tungsten powders) were mechanically milled in a high-energy attritor mill for 35 h. Ultra-fine tungsten powders and commercial Ni, Fe powders were consolidated into green compacts by using CIP method and liquid-phase sintering at 1 465 ℃ for 30 min in the dissociated ammonia atmosphere. Liquid-phase sintered tungsten heavy alloys using ultra-fine tungsten powders exhibit full densification (above 99% in relative density) and higher strength and elongation compared with conventional liquid-phase sintered alloys using original tungsten powders due to lower sintering temperature at 1 465 ℃ and short sintering time. The mechanical properties of sintered tungsten heavy alloy are found to be mainly dependent on the particles size of raw tungsten powders and liquid-phase sintering temperature.

Microstructure and mechanical properties of TiAl-based alloy prepared by double mechanical milling and spark plasma sintering

A fine-grained TiAl alloy with a composition of Ti-45Al-2Cr-2Nb-1B-0.5Ta-0.225Y （mole fraction, %） was prepared by double mechanical milling（DMM） and spark plasma sintering（SPS）. The relationship among sintering temperature, microstructure and mechanical properties was studied. The results show that the morphology of double mechanical milled powder is regular with size in the range of 20-40 μm and mainly composed of TiAl and Ti3Al phases. The main phase TiAl and few phases Ti3Al, Ti2Al and TiB2 were observed in the SPSed alloys. For samples sintered at 900 ℃ the equiaxed crystal grain microstructure is achieved with size in the range of 100-200 nm. With increasing the SPS temperature from 900 ℃to 1000 ℃ the size of equiaxed crystal grain obviously increases, the microhardness decreases from HV658 to HV616, and the bending strength decreases from 781 MPa to 652 MPa. In the meantime, the compression fracture strength also decreases from 2769 MPa to 2669 MPa, and the strain to fracture in compression increases from 11.69% to 17.76%. On the base of analysis of fractographies, it shows that the compression fracture transform of the SPSed alloys is intergranular rupture.

Microstructure and mechanical properties of Ti-43Al-9V alloy fabricated by spark plasma sintering

A fine-grained TiAl alloy with the composition of Ti-43Al-9V was prepared by mechanical milling and spark plasma sintering（SPS）.The relationship among sintering temperature,microstructure and mechanical properties was studied.The results show that the morphology of mechanical milling powder is regular with size in a range of 5-30 μm.Main phases of γ-TiAl,α2-Ti3Al and few B2 phase are observed in the SPS bulk samples.For samples sintered at 1150 °C,equiaxed crystal grain microstructure is achieved with size in a range of 300 nm-1 μm.With increasing SPS temperature to 1250 °C,the size of equiaxed crystal grains obviously increases,the microhardness decreases from HV592 to HV535,and the bending strength decreases from 605 to 219 MPa.Meantime,the compression fracture strength also decreases from 2601 to 1905 MPa,and the strain compression decreases from 28.95% to 12.09%.

Effect of spark plasma sintering temperature on microstructure and mechanical properties of melt-spun TiAl alloys

A TiAl alloy from pulverized rapidly solidified ribbons with the composition of Ti-46Al-2Cr-4Nb-0.3Y（mole fraction,%） was processed by spark plasma sintering（SPS）.The effects of sintering temperature on the microstructure and mechanical properties were studied.The results show that the microstructure and phase constitution vary with sintering temperature.Sintering the milled powders at 1200 ℃ produces fully dense compact.Higher sintering temperature does not improve the densification evidently.The dominant phases are γ and α2 in the bulk alloys sintered at 1200 ℃.With higher sintering temperature,the fraction of α2 phase decreases and the microstructure changes from equiaxed near γ grain to near lamellar structure,together with a slight coarsening.The bulk alloy sintered at 1260 ℃ with refined and homogeneous near lamellar structure reveals the best overall mechanical properties.The compressional fracture stress and compression ratio are 2984 MPa and 41.5%,respectively,at room temperature.The tensile fracture stress and ductility are 527.5 MPa and 5.9%,respectively,at 800 ℃.

Investigation on sintering and deformation strengthening of Mo-Cu alloy

Mo-Swt%Cu nanocomposite powders were fabricated by mechanical alloying, and full density alloy was obtained via liquid-phase sintering and post-treatment process. The microstructure of Mo-8wt%Cu alloy was investigated by scanning elec-tron microscope （SEM） , and the effects of process parameters on relative density, tensile strength and elongation were stud-ied. The results indicate that the relative density of Mo-Cu alloy is 98. 6% after sintering at 1 250℃ for 30 min, and its micro-structure is composite network The full density of Mo-Cu alloy can be obtained when specimens are treated through deforma-tion strengthening process of rotating forging and hydrostatic extrusion The tensile strength and elongation rate are 576 MPa and 5. 8% ,respectively, when hydrostatic extrusion deformation degree is 40%.

Effect of mechanical alloying and sintering process on microstructure and mechanical properties of Al-Ni-Y-Co-La alloy

Al86Ni7Y4.5Co1La1.5 （mole fraction, %） alloy powder was produced by argon gas atomization process. After high-energy ball milling, the powder was consolidated by vacuum hot press sintering and spark plasma sintering （SPS） under different process conditions. The microstructure and morphology of the powder and consolidated bulk sample were examined by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. It is shown that amorphous phase appears when ball milling time is more than 100 h, and the bulk sample consolidated by SPS can maintain amorphous/ nanocrystalline microstructure but has lower relative density. A compressive strength of 650 MPa of Al86Ni7Y4.5Co1La1.5 nanostructured samples is achieved by vacuum hot extrusion （VHE）.