纯钨零件的粉末注射成形工艺研究

本文以高能球磨钨粉和高纯钨粉为原料,采用粉末注射成形技术成功制备出具有复杂形状的纯钨及添加稀土的钨零件。重点研究了注射成形工艺参数对其微观结构及其力学性能的影响规律。研究结果表明,以高能球磨后的钨粉和Y2O3为原料,采用注射成形工艺可制备出烧结密度为18．26g／cm^3,相对密度为94．61％的钨零件,较佳的工艺参数为：粉末装载量为52％,注射温度为165℃,注射压力为65MPa,烧结温度为2300℃。研究结果还表明：稀土元素氧化物的添加,可显著提高注射成形钨零件的烧结密度,明显细化烧结后样品的晶粒。这是由于稀土氧化物作为第二相粒子弥散分布于晶界处,阻碍了位错的运动和高温烧结时晶粒的长大。     

Processing of Net‐shaped Nanocrystalline Fe‐Ni Material

Development of nanoparticulate materials technology is essential to processing of highly functional nanoparticulate materials and components with small and complex shape. This paper provides an overview on our recent investigations on the processing of net‐shaped nanocrystalline Fe‐Ni powder and related material property such as mechanical property. The key‐processing concept is the synthesis of nanopowders and subsequent consolidation with controlled microstructure by using powder injection molding (PIM) process. Especially, the pressureless sintering process is inevitable for consolidation of the PIMed nanopowder. The present review focuses on the densification process and related mechanical property of the PIMed Fe‐Ni nanopowder in association with microstructural evolution and diffusion process.     

陶瓷微结构件的注射成形工艺及其微观组织

采用粉末微注射成形技术制作了ZrO2陶瓷微结构件,分析了其注射成形工艺,包括喂料配制、注射工艺及烧结工艺对微观组织的影响.实验结果表明,粉末体积分数为55%的生坯注射成形后在1 500℃下烧结2 h,采用排水法测得其微结构相对密度高达98.5%,采用纳米硬度分析法得到其微结构的显微硬度值为13.75 GPa.扫描电子显微镜(SEM)结果表明,提高模具温度和注射压力,有利于微结构的填充,进而改善微结构件的微观组织;高的烧结温度可以增加零件的致密度,但容易导致晶粒的过度长大和尺寸不均匀.激光共聚焦光学显微镜观察结果表明,使用亚微米级陶瓷超细粉得到的微结构具有良好的表面质量,其烧结前、后的表面粗糙度值分别为0.33μm和0.28μm.此外,提高粉末含量可以减小零件收缩率,从而有利于微结构的尺寸精度控制.     

Effects of Cu on Microstructures,Mechanical, and Magnetic Properties of Fe–Ni–P Alloys Fabricated by Liquid Phase Sintering

The Fe–Ni–P–Cu alloys with different copper content (0, 0.5, 1, and 2 wt%) are fabricated by liquid phase sintering (LPS) at 950 °C. The nano‐Cu powder is mechanically mixed for 90 min with Fe–Ni–P composite powder using the ethanol as the medium. The microstructure, microhardness and compressive properties of Fe–Ni–P–Cu alloys are investigated. The results indicate that the copper is beneficial to improve the mechanical properties of sintered specimens. The sample contains a small amount of γ‐(Fe, Ni) phase when the copper content is 1 wt%, which results in its the highest compressive yield strength (948.1 MPa). The highest microhardness of 371 HV is accessible in Fe–Ni–P–Cu alloy with 2 wt% Cu. The fracture surface analysis indicates that sintered specimens with Cu addition exhibit a typical intergranular mode.     

The effect of nano-sized stainless steel powder addition on mechanical and physical properties of micropowder injection molded part

Micropowder injection molding (μPIM) is a new technology that has potential in the mass production of microcomponents. A bulk material of nanoparticles possesses completely different properties from those of large-sized particles. The main objective of this study is to study the effects of nano-sized powder addition on the μPIM process of powder-polymer mixtures for the fabrication of miniature parts. The binder systems consist of polyethylene glycol (PEG), polymethyl methacrylate (PMMA), and stearic acid (SA) with different powder loading blended with powders. The results indicate that increasing the nanopowder content to 30 wt.% increased the powder loading and decreased the injection and sintering temperatures. The sintered parts had densities of 96% of the theoretical value. High physical and mechanical properties of the sintered specimen were achieved with the 30 wt.% nano-sized powder sintered at 1200 °C at a heating rate of 5 °C/min under vacuum atmosphere. A significant reduction of the surface roughness of the sintered parts using the nano–microhybrid powder (S_a = 0.365 μm) was observed compared with the sintered parts with only micropowder (S_a = 1.002 μm). Using nanopowders, the hardness also increased from 182 HV to 221 HV with a linear shrinkage of approximately 9%, which is less than that of the micropowders (18%).     

Microstructure and mechanical properties of spark plasma sintered austenitic ODS steel

In this work, austenitic oxide dispersion strengthened (AODS) steel of composition Fe–16Cr–16Ni–1.5 W–0.21Ti–0.3Y₂O₃ (wt. %) was fabricated using two–stage ball milling followed by consolidation through spark plasma sintering (SPS). In the first–stage, mechanical alloying (MA) of ferritic powder and nano sized Y₂O₃ was carried out. This was followed by the addition of Ni in second–stage milling. SPS of the milled powder was carried out at 900, 950, 1000 and 1050 °C to explore the role of SPS temperature on density, microstructure as well as mechanical properties of the consolidated samples. A relative density of ～ 99% was obtained for samples sintered at 950 and 1000 °C. The as–sintered samples were subsequently solution annealed at 1075 °C for 2 h and water quenched. X–ray diffraction studies confirmed the presence of austenite in the consolidated and solution annealed samples. Electron back scatter diffraction analysis of solution annealed samples sintered at all the temperatures revealed a bimodal microstructure. The average grain size of 1.07 ± 0.72 µm was obtained for solution annealed samples sintered at 1000 °C. Yield strength and elongation of the same was measured as 851 MPa and 18%, respectively at room temperature. These values are the best combination of strength to elongation achieved on AODS alloys processed using MA and SPS, which makes this AODS steel much promising for high temperature applications.     

Densification behavior,mechanical properties and thermal shock resistance of tungsten alloys fabricated at low temperature

The low-temperature shrinkage of tungsten was greatly accelerated by the addition of trace Nb and Ni, and the addition of trace Nb and Ni also significantly promoted the final sintering density. The 99.1% of theory density for W–0.1 wt.%Nb–0.1 wt.%Ni material sintered at 1600 °C was obviously greater than 93.7% of theory density for W material sintered at 2000 °C. Ball milling treatment played an important role in promoting the sintering densification of W–0.1 wt.%Nb–0.1 wt.%Ni powder, and the powder milled for 10 h (W10) could be sintered to near full density (99.4% of theory density) at 1600 °C. The ball milling for 15 h has no effect in improving the sintering density, but it induced rapid growth of tungsten grains. The microhardness and tensile strength of the sintered tungsten alloys were highly dependent on its sintering density and grain size. Improving the sintering density while controlling the grain growth could effectively promote the microhardness and tensile strength. Furthermore, the improvement of thermal shock resistance of the W10 alloy was due to good microstructure and the increase in the tensile strength.     

Densification Behavior and Wear Response of Spark Plasma Sintered Iron‐Based Bulk Amorphous Alloys

In the present study, spark plasma sintering (SPS) process is used to sinter Fe‐based bulk amorphous alloys from starting amorphous powder. The sintering was performed in supercooled liquid region (at 630 °C with uniaxial pressure of 70 MPa) where plastic flow of the amorphous powder results in better densification without crystallization. To study the crystallization behavior and its influence on mechanical behavior, the sintered discs were de‐vitrified by annealing at 700 and 800 °C. Detailed characterization of phase development, microhardness at different loads, and wear behavior of the as‐sintered and annealed alloys is presented.     

金属粉末注射成形钛合金工艺研究

为了探究保障最终产品性能满足ASTM标准的粉末注射成形工艺,本文采用金属粉末注射成形方法,以德国Basf公司提供的喂料为原料,通过对注射参数优化获取1组最优注射工艺参数,用于后续脱脂及烧结工艺.利用拉伸、弯曲等力学实验,扫描电镜、金相光学显微镜等表征方法对材料的力学性能及微观结构进行表征,研究了注射、脱脂和烧结工艺参数...     

Fracture toughness determination and microstructure investigation of a B4C–NanoTiB2 composite with various volume percent of Fe and Ni additives

Boron carbide (B₄C) has wide application in manufacturing of abrasives and cutting tools, due to its unique features such as high hardness, good wear resistance, low specific weight and chemical stability. An additive reinforcing phase and sintering aids are used to improve its sinterability. In the present paper, a B₄C composite with 10 vol.% of titanium diboride nanoparticles (TiB₂) and a 0, 1.5 and 2.5 vol.% iron or nickel metallic additive, respectively, was mixed in an isopropanol environment containing tungsten carbide pellets. After drying, the obtained mixture was formed by cold pressing. The obtained parts were sintered at 2400 °C. The effect of adding metallic sintering aids on the mechanical properties and microstructure of the composite was investigated and fracture toughness values were evaluated by indentation test method. Addition of Fe and Ni improved values for density, hardness, Young’s modulus and fracture toughness, with Ni addition increasing the values considerably. Scanning electron microscope (SEM) images of the microstructure of the specimens showed the arrangement posture of the additives and confirmed the results obtained. Additionally, the FeB and Ni₃B blades formation were observed from the images.     

Sintering properties of submicron TiC powders from carbon coated titania precursor

The sintering behavior of submicron titanium carbide (TiC) synthesized from carbon coated titania (TiO₂) precursor was investigated in TiC-Ni system. The densification was examined as functions of initial carbon content (30.95–34 wt.%) and Ni content (3–20 wt.%). The sintered density of TiC-Ni was markedly decreased with increased carbon content in the precursor. The amount of Ni had a relatively small influence on the densification of submicron TiC-Ni cermet compared with TiC (commercially available HCS)-Ni cermets. The results show that submicron TiC with only 3 wt.% Ni can be sintered to densities above 95% TD in flowing Ar+10H₂ at 1500°C and below. The improvements in densification result from the capillary force increase since it is inversely dependent on the particle size. With decreased Ni content, the Vickers hardness increased and the fracture toughness decreased, as expected. However, the sufficient densification cannot be achieved for commercial HCS TiC powder sintered with Ni (<10 wt.%) under the same conditions. Therefore, both the Vickers hardness and fracture toughness decreased as the Ni content decreased. This was due to the increase of porosity in the sintered samples containing commercial TiC powder.     

Synthesis and microstructural characterization of Al–Ni3Al composites fabricated by press-sintering and shock-compaction

Aluminum matrix composites reinforced with nanocrystalline Ni3Al intermetallic particles, were synthesized using powder metallurgy techniques. Nanocrystalline Ni3Al was obtained by mechanical alloying of Ni75–Al25 stoichiometric mixture from elemental powders after 900 ks of milling with a 5 nm grain size average. Mixture powders of aluminum with 0.007, 0.02 and 0.04 volume fractions of Ni3Al intermetallic particles were compacted using two different compaction methods, the cold isostatic press and sintered at 873 K and the shock-compaction technique. Microstructure of shock-compacted composites showed fine particles of a few microns and also coarse particles less than 100 μm homogeneously distributed on the matrix, also the presence of micro-cracks and low porosity. However the nanoscale features of intermetallic was retained. On the other hand, the press and sintered composites showed good densification. The densities of the composites were about 90% and 94% of the theoretical density for the shock-compacted and press-sintered process, respectively. Finally, the results of hardness measurements showed that the nanocrystalline Ni3Al reinforcement improves the hardness of Al matrix for all conditions. The highest hardness was obtained for the Al–4 vol.%Ni3Al shock-compacted composite.     

Metal injection molding of pure molybdenum

In this work the processing steps for producing molybdenum parts by means of metal injection molding technique, including milling, mixing, debinding and sintering, were investigated in detail. Different feedstocks were prepared from received and milled molybdenum powder and a thermoplastic binder based on paraffin wax. The feedstock including 50% by volume of milled molybdenum powder had better rheological property and was injected successfully at low pressure. The molded specimens were debinded by two different processes, direct thermal debinding and solvent–thermal debinding. The content of carbon and oxygen were respectively less than 0.060% and 0.0042% after the parts were sintered under hydrogen atmosphere. The parts sintered at 1850 °C for 120 min exhibited a highest density of 9.70 g/cm³,meanwhile the tensile strength and hardness was 229 MPa and 193 HV10, respectively.     

Experimental study on the plastic deformation and densification characteristics of some sintered and heat treated low alloy powder metallurgy steels

Sintered low alloy steels containing the alloying elements molybdenum, copper and titanium were synthesised through powder metallurgy route from mixed elemental powders to yield the compositions: Fe–0.5% C, Fe–0.5% C–2% Cu, Fe–0.5% C–2% Mo and Fe–0.5% C–2% Cu–2% Mo–2% Ti. Green cylindrical compacts were made using a 1000 kN hydraulic press using suitable cylindrical die-punch combination. The ceramic coated cylindrical preforms were sintered at 1000 ± 10 °C in a muffle furnace for a period of 120 min. After sintering, the preforms were subjected to different heat treatment processes, namely, heating to 900 °C, soaking for 60 min and quenching in air or oil or cooled inside the furnace. The heat treated preforms were subject to axial upsetting deformations, at various applied loads and their densification behaviours were compared. The influence of various heat treatment processes on deformation and densification of the alloys was studied and correlated with their microstructures. The plain carbon steel preforms were observed to respond well to the three heat treatment cycles by way of exhibiting the highest levels of densification and plastic deformation. However, both alloy addition and heat treatment have led to a reduction in densification and deformation of the alloy steel preforms. Presence of titanium carbide particulates in the microstructure of the Ti-alloyed steel has played a significant role in reducing the densification as well as deformation. The basic ferritic–pearlitic microstructure of Fe–0.5% C steel has essentially promoted the largest deformation levels coupled with higher densification.     

Application of metal injection molding process to fabrication of bulk parts of TiAl intermetallics

In the present study, a metal injection molding (MIM) process was applied to the fabrication of bulk parts of TiAl intermetallics, and effects of sintering parameters on densification of fabricated parts were investigated. The specimens sintered at 1350 °C showed about the same densification as the ones sintered at 1400 °C, while grains and pores were finer, and thus 1350 °C was chosen as the sintering temperature. In the sintered specimens after debinded in an H₂ atmosphere, Al₂O₃ precipitates were observed around pores. The densification decreased with increasing heating rate up to the sintering temperature. It was also found that the sintering time increased the densification without grain coarsening. The optimal heating rate was found to be 3 °C/min, and the densification reached a near-full level of 98.8% when sintered at 1350 °C for 30 h. These findings suggested a useful idea to successfully fabricate TiAl intermetallic parts by the MIM process.     

搅拌球磨制备亚微米晶粒Ti(C,N)基金属陶瓷

用搅拌球磨方法制备了亚微米TiC-TiN-WC-Mo-Ni-C金属陶瓷复合粉，并烧结成亚微米晶粒Ti(C,N）基金属陶瓷；研究了原始粉末粒度，磨球大小，球磨时间对复合粉粒度的影响，研究了球磨过程中氧和铁元素对粉末的污染情况；并对烧结合金的组织，性能进行了分析，表明亚微米晶粒Ti(C,N）金属陶瓷的性能优良。     

Structure and thermal conductivity of powder injection molded AlN ceramic

AlN powders doped with Y₂O₃ (5 wt.%) were compacted by employing powder injection molding (PIM) technique. The binder consisted of paraffin wax (PW, 60 wt.%), polypropylene (PP, 35 wt.%) and stearic acid (SA, 5 wt.%). The feedstock was prepared with a solid loading of 62 vol.%. The binder was removed through debinding process in two steps, solvent debinding followed by thermal debinding. At last, the debound samples were sintered in flowing nitrogen gas at atmospheric pressure. The result reveals that thermal debinding atmosphere has significant effect on the thermal conductivity and structure of AlN ceramics. The thermal conductivity of injection molded AlN ceramics thermal debound in flowing nitrogen gas is 231 W m^?1 K^?1.     

Effect of temperature-related factors on densification,microstructure and mechanical properties of powder metallurgy TiAl-based alloys

In the present work, the influence of temperature-related factors, including sintering temperature, heating step and temperature-control mode, on the densification, microstructure and mechanical properties of Ti-46.5Al-2.15Cr-1.90Nb-(B, Y, Mo) alloys prepared by SPS has been investigated and discussed in detail. The results obviously indicate that the sintering temperature plays a key role on densification and phase transition, when compared with the heating step and temperature-control mode. Based on the experimental results and theoretical analysis, the densification process and microstructural evolution of TiAl-based alloys during sintering are studied. Moreover, the mechanical properties of the sintered alloys are determined by the combined effects of the densification and microstructure. The obtained results will help to optimize the microstructure and properties for this kind of intermetallic alloys through controlling sintering parameters during powder metallurgy process.     

Effect of Ni on Sintering Characteristics of Short Cast Iron Fibre

Nickel,as the carrier through which Fe atomsdiffuse,obviously enhances the densification ofsintered compact containing short cast iron fibre.When Ni content is above 4.5 wt-% there are someaustenites in microstructure at room temperature,discontinuous cementite networks at the interfacesbetween austenites and pearlites,free graphite pre-cipitated in austenite and pores andWidmannst(?)tten carbide precipitated in austenite.When Ni content is about 12 wt-%,it leads to de-crease in densification ratio and change in fracturemorphology of sintered compact from ductile tobrittle.     

Production of injection moulded 316L stainless steels reinforced with TiC(N) particles

Abstract

Metal matrix composites, based on 316L stainless steel and reinforced with TiC and TiCN particles, were manufactured following a powder injection moulding route: mixing, preparation of feedstock, moulding, debinding and sintering. The 316L stainless steel and carbide powders were dry mixed and moulded with wax based binder. The critical powder loading for injection moulding was 62·5 vol.-% for all samples. Binder debinding was performed by solvent and thermal method. After debinding, the samples were sintered at 1250 and 1385°C for 1 h in pure H₂. Metallographic studies were conducted to extend densification and the corresponding microstructural changes. The sintered samples were characterised by measuring tensile strength, hardness and wear behaviour. Wear loss was determined for all samples after wear tests. All powder, fracture surfaces of moulded and sintered samples, and worn surfaces of all the samples, were examined using scanning electron microscope. The sintered density of injection moulded 316L stainless steel samples, reinforced and unreinforced, increases with increasing sintering temperature. The addition of TiC and TiCN improves the hardness and wear resistance with increasing sintering temperature.