粉末冶金FeCoNiCu0.4Al0.4高熵合金的热处理组织与性能

采用机械合金化(MA)与放电等离子烧结(SPS)相结合的方法制备出FeCoNiCu0.4Al0.4高熵合金,研究不同热处理温度对合金显微组织与力学性能的影响规律。结果表明:机械合金化后,FeCoNiCu0.4Al0.4高熵合金形成了单相的FCC固溶体,经1100℃SPS烧结后的块体组织仍为单相FCC结构,其压缩屈服强度、塑性应变和显微硬度分别为1165.1 MPa、45.2%和356.9 HV。经过热处理后,合金组织中生成了新的BCC相,且BCC相的含量随热处理温度的升高先增多后减少,500、600和700℃热处理后BCC相的含量分别为7%、30%和21%(体积分数)。退火态FeCoNiCu0.4Al0.4高熵合金的屈服强度随热处理温度的升高先升高后降低。当BCC相含量增多时,材料的屈服强度和硬度相应地提高,而塑性却显著降低。     

烧结方式对CoCrNi中熵合金组织及力学性能的影响

采用机械合金化法（MA）球磨制备CoCrNi中熵合金原料粉末,结合放电等离子烧结（SPS）或高真空烧结制取CoCrNi中熵合金,研究了球磨时间以及退火对CoCrNi中熵合金原料粉末微观形貌、颗粒尺寸及相结构的影响规律,对不同烧结方式制备的合金块体进行微观结构及力学性能研究。结果表明：随着球磨时间的延长,各单质粉末颗粒尺寸不断减小并逐渐融合,在球磨25 h后,原料粉末主要为fcc固溶体结构,还有少量的bcc相;在后续烧结过程中,少量bcc相发生相转变,组织中只有fcc相结构;退火烧结样品的弹性模量为6.57 GPa,是真空烧结的1.55倍,屈服强度为279.28 MPa,与真空烧结后样品的屈服强度相当,退火烧结的延伸率为35.97%,明显大于直接真空烧结;SPS烧结的块体合金表现出高达793.72MPa的屈服强度和61.08%的塑性应变,且维氏硬度(HV)达到3910.2MPa,与其它2种烧结方法相比,SPS在实现高熵合金（HEAs）快速低温烧结方面更具潜力。     

Alloying behavior and novel properties of CoCrFeNiMn high-entropy alloy fabricated by mechanical alloying and spark plasma sintering

An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a solid solution with refined microstructure of 10 nm which consists of a FCC phase and a BCC phase was formed. After SPS consolidation, only one FCC phase can be detected in the HEA bulks. The as-sintered bulks exhibit high compressive strength of 1987 MPa. An interesting magnetic transition associated with the structure coarsening and phase transformation was observed during SPS process.     

Effect of Spark-Plasma-Sintering Conditions on Tensile Properties of Aluminum Matrix Composites Reinforced with Multiwalled Carbon Nanotubes (MWCNTs)

In this study, aluminum (Al) matrix composites containing 2 wt.% multiwalled carbon nanotubes (CNTs) were fabricated by powder metallurgy using high-energy ball milling (HEBM), spark plasma sintering (SPS), and subsequent hot extrusion. The effect of SPS conditions on the tensile properties of CNT/Al composites was investigated. The results showed that composites with well-dispersed CNTs and nearly full-density CNT/Al can be obtained. During HEBM, CNTs were shortened, inserted into welded Al powder particles, bonded to Al, and still stable without CNT-Al reaction. After consolidation, Al₄C₃ phases formed in composites under different sintering conditions. With the increase of sintering temperature and holding time, the strength decreased. Conversely, the ductility and toughness noticeably increased. As a result, a good balance between strength (367 MPa in ultimate tensile strength) and ductility (13% in elongation) was achieved in the as-extruded CNT/Al composite sintered at 630°C with a holding time of 300 min.     

Microstructural and mechanical evaluation of Al-TiB2 nanostructured composite fabricated by mechanical alloying

Production of bulk Al-TiB₂ nanocomposite from mechanically alloyed powder was studied. Al-20 wt.% TiB₂ metal matrix nanocomposite powder was obtained by mechanical alloying (MA) of pure Ti, B and Al powder mixture. A double step process was used to prevent the formation of undesirable phases like Al₃Ti intermetallic compound, which has been described in our previous papers. The resultant powder was consolidated by spark plasma sintering (SPS) followed up by hot extrusion. The structural characteristics of powder particles and sintered samples were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Hardness measurements were conducted on the cross section of powder particles and sintered sample and the tensile behavior of extruded samples was evaluated. The results showed that the prepared Al-20 wt.% TiB₂ nanocomposite has good thermal stability against grain growth and particle coarsening. Extruded Al-20 wt.% TiB₂ showed a hardness value of 180 VHN and yield and tensile strength of 480 and 540 MPa, respectively, which are much higher than those reported for similar composites made by other processes.     

Nanostrucmred A1-Zn-Mg-Cu alloy synthesized by cryomilling and spark plasma sintering

Nanocrystallized Al-10.0%Zn-3.0%Mg-1.8%Cu (mass fraction) alloy powder was prepared by cryomilling, and then the nanostructured powder was consolidated into bulk material by spark plasma sintering (SPS). The microstructural evolution and phase transformation were studied. A supersaturated face-centered cubic solid solution is formed after cryomilling for 10 h, and the average grain size is 28 nm. Two typical nanostructures of the bulk nanostructured alloy are observed: primarily equiaxed grains with size of 150 nm, and occasionally occurring sub-micron grains up to 500 nm. Two types of MgZn₂ particles precipitate during consolidation. One is the sub-micron particles distributed along the boundaries of the powders, and the other is fine particles with size of several nanometers in the matrix, especially at the boundaries of sub-micron grains. These second phase particles can be completely dissolved into matrix by proper solid solution treatment.     

Reactive Atmospheric Plasma Spraying of AlN Coatings: Influence of Aluminum Feedstock Particle Size

Feedstock powder characteristics (size distribution, morphology, shape, specific mass, and injection rate) are considered to be one of the key factors in controlling plasma-sprayed coatings microstructure and properties. The influence of feedstock powder characteristics to control the reaction and coatings microstructure in reactive plasma spraying process (RPS) is still unclear. This study, investigated the influence of feedstock particle size in RPS of aluminum nitride (AlN) coatings, through plasma nitriding of aluminum (Al) feedstock powders. It was possible to fabricate AlN-based coatings through plasma nitriding of all kinds of Al powders in atmospheric plasma spray (APS) process. The nitriding ratio was improved with decreasing the particle size of feedstock powder, due to improving the nitriding reaction during flight. However, decreasing the particle size of feedstock powder suppressed the coatings thickness. Due to the loss of the powder during the injection, the excessive vaporization of fine Al particles and the completing nitriding reaction of some fine Al particles during flight. The feedstock particle size directly affects on the nitriding, melting, flowability, and the vaporization behaviors of Al powders during spraying. It concluded that using smaller particle size powders is useful for improving the nitriding ratio and not suitable for fabrication thick AlN coatings in reactive plasma spray process. To fabricate thick AlN coatings through RPS, enhancing the nitriding reaction of Al powders with large particle size during spraying is required.     

Thermal sprayed stainless steel/carbon nanotube composite coatings

Stainless steel/carbon nanotube (SS/CNT) composite coating was prepared by thermal spray from the feedstock powder synthesized by chemical vapor deposition at a synthesis temperature and time of 800 °C and 120 min under ethanol atmosphere. Microstructural investigation by TEM and SEM revealed that grown CNTs covering the surface of stainless steel particles were multi-walled type with an average diameter of about 44 nm. Microstructures of pure stainless steel and SS/CNT composite coatings similarly showed splat characteristic and lamellar structure. Incorporation of CNTs was clearly observed in the composite coating. Hardness of SS/CNT composite coating (480 ± 36 HV_0.3) was higher than that of pure stainless steel coating (303 ± 33 HV_0.3). Coefficient of friction of the SS/CNT coating was almost 3 times lower than that of stainless steel coating which resulted in reduction of sliding wear rate of nearly 2 times. This research thus demonstrated a new composite coating with better wear resistive performance compared to a coating deposited by commercially available stainless steel powder.     

Investigation of Deposition Behavior of Cold-Sprayed Magnesium Coating

Two types of magnesium powders with different particle size distributions were deposited by cold spraying at different main gas temperatures. The effects of gas temperature and particle size distribution on the deposition efficiency of particles were studied. The microstructure of coatings was observed, and the porosity of coatings was evaluated. The deposition efficiency of particles increased, and the porosity of coatings decreased with the increase of gas temperature. The deposition efficiency of particles increased when using the powder with a smaller particle size distribution. Stainless steel and aluminum plates were used as substrates. The bonding strength and mechanism between the coating and substrate were studied. The commercial finite element software ABAQUS was used to help us better understand the deformation behavior of particles and substrates. The mean bonding strength slightly increased when aluminum plates were used as substrates. The bonding mechanism of Mg coatings on stainless steel and aluminum substrates was discussed.     

Effects of WC particle size on densification and properties of spark plasma sintered WC–Co cermet

The WC–Co cermet bulks were prepared by spark plasma sintering (SPS) using powder mixtures with different-scaled WC particles. The SPS densification process was studied by calculating the current distribution between the powder sample and the die in the SPS system. The microstructures were characterized and compared for different samples by the WC grain size, Co mean free path and contiguity of WC grains. In spite of a weak effect of WC particle size on the SPS densification stages, the WC particle size plays a significant role in the homogeneity of the cermet microstructure. Good mechanical properties of the SPSed cermet were obtained with an optimized WC and Co particle-size combination. The effects of scale combination of WC and Co particles on the microstructure hence the properties of the SPSed cermet were discussed.     

Nanostructured metal composites reinforced with fullerenes

This work presents the results of the characterization of nanostructured Al or Fe matrix composites reinforced with fullerenes. The fullerene used is a mix of 15 wt%C₆₀, 5 wt.%C₇₀, and 80 wt.% soot that is the product of the primary synthesis of C₆₀. The composites were produced by mechanical alloying and sintered by spark plasma sintering (SPS). It was found that in both composites, C₆₀ withstands mechanical alloying, and acts as a control agent, reducing the agglomeration of the particles. In both composite systems the as-mechanically alloyed powders as well as the SPS sintered products are nanostructured. During the SPS process the effect of the metal (Al or Fe) matrix with the fullerene is different for each composite. For instance, Al reacts with all the carbon in the fullerene mix and forms Al₄C₃; on the contrary, in the Fe-fullerene composite, Fe sponsors the synthesis of C₆₀ during the SPS process. The synthesis of the C₆₀ is presumably assisted by the catalytic nature of Fe and the electric field generated during the SPS sintering process.     

Spark plasma sintering behavior of pure aluminum depending on various sintering temperatures

We have successfully fabricated high-density pure aluminum (Al) bulk by means of a spark-plasma-sintering (SPS) process. The relative density of Al was enhanced as the sintering temperature of the SPS process increased. During the SPS process for pure Al power, the Al oxide layer on the surface of the Al particle was partially broken by the microplasma and applied pressure. The microstructures of the spark-plasma-sintered compacts obtained at various temperatures were observed by optical microscopy, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. We believe that the pinning effect, rapid heating cycle, and applied pressure played an important role in restraining the particle growth despite the increase in sintering temperature. It is feasible that the employed SPS process could be very useful to achieve fully densified Al compact.     

火花等离子烧结技术制备的WC/Co纳米硬质合金

研究了火花等离子烧结工艺与YG10、YG12两种纳米硬质合金性能的关系.然后采用火花等离子烧结技术制备了硬质合金功能梯度材料,该材料由纳米WC/10%Co、纳米WC/12%Co、微米WC/15%Co混合粉以及不锈钢圆片烧结而成.显微硬度压痕显示该材料各层间的应力较小.     

Microstructural evolution and mechanical properties of a β-solidifying γ-TiAl alloy densified by spark plasma sintering

This study deals with the densification of a pre-alloyed Ti–44Al–6Nb–1Mo–0.2Y–0.1B (at.%) powder by spark plasma sintering (SPS). The powder was produced by a plasma rotating electrode process (PREP), and then SPS densified at temperatures between 1200 and 1320 °C. At SPS temperatures below 1240 °C, the α₂-dominated dendritic structure in the PREP powder particles disappeared and the fully dense microstructure mainly consisting of γ and B2 grains formed during SPS, but several original powder particle boundaries (OPBs) still remained. While sintered above 1240 °C, OPBs vanished entirely and an uniform duplex microstructure emerged. Furthermore, fully-lamellar (FL) microstructure with mean colony size smaller than 20 μm was produced via β-homogenization annealing. This FL microstructure renders a good tensile elongation of 1.25% and yield strength of 665 MPa at room temperature. However, instability of α₂/γ lamellar structures was induced by final stabilization annealing, resulting in sharp reduction of both room-temperature ductility and high-temperature strength.     

基于SPS技术的异种钢焊接

采用SPS技术进行了异种钢的焊接研究.在不同的SPS工艺参数下实现了45钢/18-8不锈钢的焊接,对焊接接头的显微组织、化学成分、断口特征及显微硬度分布进行了分析,研究了SPS焊接工艺参数对接头组织和性能的影响规律,并提出了SPS焊接的冶金结合机理.结果表明,SPS技术作为一种全新的材料焊接方法,可以在短时、低温、低压下实现异种钢的良好扩散焊接;SPS工艺中温度对焊接接头组织和性能的影响最大,保温时间和加载压力的影响相对较小.     

An Evaluation of Dissociated Ammonia and Hydrogen Atmospheres for Sintering Stainless Steel

The effect of sintering types 302, 302B, and 430 stainless steel powder compacts in hydrogen and dissociated ammonia was investigated. It was found that sintering in dissociated ammonia resulted in as much as 0.5 wt pet increase in the nitrogen content of stainless steel even though the dissociation of the gas was complete. Sintering in hydrogen, on the other hand, reduced the nitrogen content of the stainless steel to less than 0.01 wt pet. In the case of the 302-type stainless steel, the low nitrogen content resulted in a material that was largely ferritic, whereas the high nitrogen content rendered the material fully austenitic. Sintering in dissociated ammonia resulted in lower density, generally lower tensile strength, less ductility, and higher hardness than sintering under equivalent conditions in hydrogen. The reduction of oxides on both stainless steel and iron particles was found to be effected by hydrogen partial pressure in the sintering atmosphere. Compacting pressure was found also to effect oxide reduction during sintering.     

Sintering of tungsten carbide particles sputter-deposited with stainless steel

The purpose of this work was to study the sintering process of WC–stainless steel AISI 304 composite powders prepared by an innovative process, which consists in the use of a magnetron sputtering to coat WC powder particles with the stainless steel elements. The sintering of pressed compacts was performed in a conventional vacuum furnace using a heating rate of 5 °C min⁻¹ until the selected maximum temperature, a holding time of 50–173 min and a sintering pressure of 2–20 Pa. For comparison, a conventional prepared WC powder with 6.5 wt.% of stainless steel AISI 304 was also studied.During the sintering of the coated powders, three different sintering stages were identified: an initial one due to solid state matter transport until ∼1150 °C, followed by two other stages where liquid phase may be already present. Very high weight losses occurred during the sintering of coated powder which was diminished by the shortening of the holding time, the increase of the pressure in the sintering furnace and the appropriate control of the sintering atmosphere. Despite the high values of weight loss, 96% of densification can be obtained at a relatively low sintering temperature, T=1325 °C, for an initial content of ∼10 wt.% of binder phase.     

机械合金化和烧结工艺对Al-Ni-Y-C0-La合金显微组织及力学性能的影响

通过气雾化方法制备Al86Ni7Y4．5Co1La1.5（摩尔分数,％）合金粉末。首先,将粉末进行不同时间的球磨,然后在不同的烧结温度及保压时间等条件下对粉末分别进行热压烧结和放电等离子烧结。通过X射线衍射仪（XRD）,扫描电镜（sEM）以及透射电镜（TEM）对粉末和块体材料的显微组织和形貌进行表征。结果表明：在特定球磨参数下球磨100h以上可以产生非晶,而且通过放电等离子烧结可以得到非晶／纳米晶块体材料,然而这种材料的相对密度较低。通过热压烧结可制备抗压强度为650MPa的Al86Ni7Y4．5Co1La1.5纳米块体材料。     

多孔化高熵合金改善Al-Si合金/钢体系润湿铺展性能机理

借助电极感应熔化气雾化法,制备了 FeCoNiCrMn高熵合金粉末;通过真空烧结技术,在钢表面制备了具有不同孔隙率和孔径的多孔高熵合金涂层. 研究了不同烧结工艺对多孔涂层孔隙率、孔径以及过渡层厚度的影响. 开展了Al-12Si合金在多孔高熵涂层钢表面的原位润湿铺展试验,探讨了多孔高熵合金涂层对表观接触角和铺展行为的影响规律,深入分析了多孔高熵结构内反应产物的显微组织和相组成. 结果表明,随着烧结温度的升高和保温时间的延长,多孔高熵合金涂层的过渡层厚度逐渐升高,孔隙率及平均孔径逐渐减少. 液态Al-12Si合金液滴在多孔涂层中微通道增强的毛细力作用下,迅速浸润到多孔结构中,并实现了材料表面的完全润湿. 在高熵合金的迟滞扩散效应与高熵效应共同作用下, 界面反应层中金属间化合物的形成受到显著阻碍,界面相结构由富Cr的FCC、富AlFe的BCC以及富AlNi的B2 + 富Al的BCC共晶状结构组成.     

FeCoCrNiAlx高熵合金的电爆合金化

电爆喷涂是一种表面改性的新方法,它是利用高电压对喷涂材料脉冲放电,瞬时大电流将其加热并发生爆炸,产生高温粒子伴随冲击波喷射到基体表面形成涂层。本文提出了电爆法制备高熵合金涂层的新工艺,利用XRD、SEM、EDS以及电流电压波形对该方法制备高熵合金涂层的可行性进行了研究。结果表明,FeCoCrNiAlx (x=0, 0.5, 1.0)合金系涂层都形成了简单的FCC、BCC及FCC+BCC结构固溶体,并且随着Al含量的增加,该涂层的相结构由FCC相逐渐向BCC相转变。涂层表面平整、致密,没有明显的裂纹,且元素均匀分布在涂层表面,并没有发现明显的元素偏聚现象。初始充电电压11kV下的能量沉积为285.770 J,平均沉积效率达到48.8%。随Al含量的增加,涂层显微硬度逐渐增大,当x=1.0时平均显微硬度达到最大值531.8HV,大约是基体显微硬度的2倍。可以看出,电爆法实现了高熵合金涂层的成功制备。