Preparation and mechanical properties of laminated zirconium diboride/molybdenum composites sintered by spark plasma sintering

Laminated ZrB₂/Mo composites, alternately consisting of matrix layers of 80 vol.% ZrB₂ + 10 vol.% nano-SiC whiskers + 10 vol.% SiC particles and Mo interlayers, with the addition of Si and B as interlayer adjusting agent, were prepared by roll-compaction and spark plasma sintering (at 1600°C) process. XRD and SEM techniques were used to characterize the phases and microstructure of the obtained composites. The results showed that without the addition of Si and B in the interlayer, interfacial debonding between the matrix layer and interlayer often occurred due to the thermal mismatch between the two kinds of layers. However, the interfacial mismatch could be effectively inhibited by the addition of Si and B to the Mo interlayers. The laminated ZrB₂/Mo composites with 6 at.% Si and 4 at.% B in the interlayers showed the highest bending strength at (451±20) MPa and the highest fracture toughness at (7.52±0.12) MPa·m^?. MoB, ZrB and Mo5SiB2 were formed by the reactions among ZrB₂, Mo and the additions.     

Microstructure and mechanical properties of silicon nitride-titanium nitride composites prepared by spark plasma sintering

Si₃N₄-TiN composites were prepared by spark plasma sintering (conventional sintering (SPS1) and in situ reaction sintering (SPS2)). Homogeneous distribution of equiaxed TiN grains in Si₃N₄ matrix results in the highest microhardness (21.7 GPa) and bending strength (621 MPa) of sample SPS1 sintered at 1550 °C. Dispersion of elongated TiN grains in Si₃N₄ matrix results in the highest fracture toughness (8.39 MPa m^1/2) of sample SPS2 sintered at 1300 °C.     

SPS制备TiNi增强镁合金复合材料的微观结构及力学性能

以AZ31镁合金为基体,TiNi形状记忆合金丝为增强体,利用放电等离子烧结法（SPS）制备了TiNi/Mg复合材料,用OM、SEM、EDS对其微观形貌进行表征,并用XRD及DSC研究TiNi丝的相变,同时对该复合材料进行准静态拉伸实验,对其室温及高温力学性能进行研究。结果表明,所制备的TiNi/Mg复合材料中界面处存在Mg、Ti、Ni元素的互扩散现象,并形成宽度约为2 μm的互扩散层;所制备的TiNi/Mg复合材料的高温力学性能高于室温,其中其屈服强度、抗拉强度及弹性模量在100℃时（分别为157 MPa,292 MPa,22 GPa）较室温分别提高了12%、33%和29%,150℃时（分别为143 MPa,251 MPa,20 GPa）较室温分别提高了2%、14%和18%。     

Microstructure and mechanical properties of CNT/Ag nanocomposites fabricated by spark plasma sintering

Carbon nanotube/silver (CNT/Ag) nanocomposites include CNT volume fraction up to 10?vol.% were prepared by chemical reduction in solution followed by spark plasma sintering. Multiwalled CNTs underwent surface modifications by acid treatments, the Fourier transform infrared spectroscopy data indicated several functional groups loaded on the CNT surface by acid functionalisation. The acid-treated CNTs were sensitised and activated. Silver was deposited on the surface of the activated CNTs by chemical reduction of alkaline silver nitrate solution at room temperature. The microstructures of the prepared CNT/Ag nanocomposite powders were investigated by high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy and X-ray powder diffraction analysis. The results indicated that the produced CNT/Ag nanocomposite powders have coated type morphology. The produced CNT/Ag nanocomposite powders were sintered by spark plasma sintering. It was observed from the microstructure investigations of the sintered materials by HRSEM that the CNTs were distributed in the silver matrix with good homogeneity. The hardness and the tensile properties of the produced CNT/Ag nanocomposites were measured. By increasing the volume fraction of CNTs in the silver matrix, the hardness values increased but the elongation values of the prepared CNT/Ag nanocomposites decreased. In addition, the tensile strength was increased by increasing the CNTs volume fraction up to 7.5?vol.%, but the sample composed of 10?vol.% CNT/Ag was fractured before yielding.     

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.     

Microstructure and mechanical properties of spark plasma sintered titanium‐added copper/reduced graphene oxide composites

Copper matrix composites were fabricated through mixing fixed amount of reduced graphene oxide and the different amounts of titanium. The dried copper/titanium/reduced graphene oxide mixture powders were firstly obtained by the wet‐mixing process, and then the spark plasma sintering process realized their faster densification. In the as‐sintered bulk composites, the layered reduced graphene oxide network, uniform titanium particles and copper‐titanium solid solution are observed in copper matrix. Investigations on mechanical properties show that the as‐prepared bulk composites exhibit the hardness and compressive yield strength compared with single reduced graphene oxide added composites. Increased titanium addition resulted into higher hardness and strength. The relevant formation and failure mechanisms of the composites and their influence on mechanical properties were discussed.     

Microstructure and wear properties of spark plasma sintered 316L-30W composites

ABSTRACT

316L-30W composites were successfully fabricated via spark plasma sintering at 1550°C to evaluate their potential as the interlayer between W and 316L stainless steel in fusion reactors. The effect of holding time on the microstructure and its subsequent effects on the fracture morphology and wear properties of the composites were investigated. The results show that more W particles melted and reacted with 316L steel as the holding time increased from 1 to 5 min. The generation of voids was mainly caused by the differences in diffusivity and the coefficient of thermal expansion between W and 316L. The 316L-30W composite held for 3 min had a smaller and more stable friction coefficient, indicating that its interface was firmly bonded and homogeneous.

This paper is part of a thematic issue on Nuclear Materials.     

放电等离子烧结Ni/TiB2-TiC复合材料微观组织及磨损性能

采用放电等离子烧结技术,以Ni、Ti、B₄C混合粉末为原料制备Ni/TiB₂-TiC复合材料,分析了Ni含量对复合材料的物相组成、组织结构、硬度和耐磨性的影响。结果表明：Ni/TiB₂-TiC复合材料主要物相为γ-Ni、TiB₂和TiC,其中TiB₂呈矩形条状和多边形状,TiC则呈现不规则块状;随着原始粉末中Ni含量的增加,TiB₂和TiC陶瓷相尺寸减小,其在Ni粘结相中的分布呈现出均匀化的趋势,复合材料更加致密。Ni含量显著影响Ni/TiB₂-TiC复合材料的耐磨性和磨损机制,Ni含量较低时（20wt%和30wt%）,复合材料摩擦系数（COF）较大且存在明显的波动,出现严重的疲劳磨损;随着Ni量的增加（40wt%）,材料的COF降低且趋于平稳,表现为微切削磨损;当Ni含量持续增加时（50wt%）,由于局部Ni的聚集导致粘着磨损产生,COF有所上升,耐磨性反而下降。     

Microstructure and mechanical properties of Al-Si-Ni-Ce alloys prepared by gas-atomization spark plasma sintering and hot-extrusion

Al-Si-Ni-Ce alloys with the composition of Al_78.5Si₁₉Ni₂Ce_0.5, Al₇₆Si₁₉Ni₄Ce₁ and Al₇₃Si₁₉Ni₇Ce₁ were atomized and then sintered by using spark plasma method. The microstructure of the as-atomized powders, sintered and hot-extruded samples was analyzed. The influences of granularity and sintering parameters including time and temperature on the density of sintered alloy were also discussed. It is shown that the atomized powders are composed of Si, Al₁₁Ce₃, Al₃Ni and alpha Al. Tiny Al₃Ni particles precipitate from supersaturated matrix near the powder boundaries during SPS. Hot-extrusion process leads to the layer structure and more homogeneous distribution of precipitates. These alloys exhibit high comprehensive mechanical properties with combination of high Vicker's micro-hardness, moderate tensile properties and elongation, which provide a novel kind of promising engineering materials.     

Microstructure and properties of spark plasma sintered AlN ceramics

Spark plasma sintering (SPS) is a newly developed technique that enables poorly sinterable aluminum nitride (AlN) powder to be fully densified. It is addressed that pure AlN sintered by SPS has relatively low thermal conductivity. In this work, SPS of AlN ceramic was carried out with Y₂O₃, Sm₂O₃ and Li₂O as sintering aids. Effects of additives on AlN densification, microstructure and properties were investigated. Addition of sintering aids accelerated the densification, lowered AlN sintering temperature and was advantageous to improve properties of AlN ceramic. Thermal conductivity and strength were found to be greatly improved with the present of Sm₂O₃ as sintering additive, with a thermal conductivity value about 131 Wm⁻¹K⁻¹ and bending strength about 330 MPa for the 2 wt% Sm₂O₃-doped AlN sample SPS at 1,780 °C for 5 min. XRD measurement revealed that additives had no obvious effect on the AlN lattice parameters. Observation by SEM showed that AlN ceramics prepared by SPS method manifested quite homogeneous microstructure. However, AlN grain sizes and shapes, location of secondary phases varied with the additives. The thermal conductivity of AlN ceramics was mainly affected by the additives through their effects on the growth of AlN grain and the location of liquid phases.     

Effect of sintering temperature on microstructures and mechanical properties of spark plasma sintered nanocrystalline aluminum

Organic-coated aluminum nano-powders were consolidated by spark plasma sintering technique with low initial pressure of 1 MPa and high holding pressure of 300 MPa at different sintering temperature. The effect of sintering temperature on microstructures and mechanical properties of the compact bulks was investigated. The results indicate that both the density and the strain of the nanocrystalline aluminum increase with an increase in sintering temperature. However, the micro-hardness, compressive strength and tensile stress of the compact bulks increase initially and then decrease with increasing sintering temperature. The nanocrystalline aluminum sintered at 773 K has the highest micro-hardness of 3.06 GPa, the best compressive strength of 665 MPa and the supreme tensile stress of 282 MPa. A rapid grain growth of nanocrystalline aluminum sintered at 823 K leads to a decrease in micro-hardness, compressive strength and tensile stress. After annealing, a remarkable increase in strain and a slight rise in strength were obtained due to the relief of the residual stress in nanocrystalline Al and the formation of composite structure.     

Microstructure and properties of Nd-Fe-B magnets prepared by spark plasma sintering

Abstract

Anisotropic Nd₁₅.₅Dy₁.₀Fe_BalCo₃.₀B₆.₈Al₁.₀ magnets were produced by the spark plasma sintering (SPS) technique. The effects of processing conditions on the microstructure, magnetic properties, dimensional precision and density of the magnets were studied. The magnetic properties, microstructure and constituents were investigated by means of a magnetic flux density - magnetic field strength (B-H) loopline instrument, scanning electron microscopy and energy dispersive X-ray analysis. The density of the magnets was determined by the Archimedes method, and the dimensional precision of the magnets was measured by micrometer. It was found that the microstructure of SPS processed Nd-Fe-B magnets is unique; the grain size is fine and uniform while distribution of the neodymium rich phase is heterogeneous. The optimal magnetic properties of SPS processed Nd-Fe-B magnets obtained so far are maximum energy product of 240 kJ m^-3 and coercive force of 1260 kA m^-1. The dimensional precision of the magnets is ~ 20 μm, and the density of the magnets reaches 7.58 g cm^-3.     

放电等离子烧结制备Diamond/Al复合材料

采用放电等离子烧结法（SPS）制备了Diamond/Al复合材料,研究了金刚石粒径、成分配比、工艺参数等对复合材料的导热性能的影响。结果表明,SPS可以得到导热性能较好的Diamond/Al复合材料,致密度是影响该材料导热性能的最重要因素。在实验确定的金刚石体积分数50%,金刚石粒径70 μm,温度550℃、压力30 MPa的工艺条件下,所制备的材料致密度较高,热导率为182 W/(m·K),比相同条件下纯铝粉烧结体的热导率提高了34.8%,表明金刚石的添加对烧结铝基材料导热性能有明显的改善作用。      

Microstructure and mechanical properties of ultra-fine grained MoNbTaTiV refractory high-entropy alloy fabricated by spark plasma sintering

The MoNbTaTiV refractory high-entropy alloy(RHEA) with ultra-fine grains and homogeneous microstructure was successfully fabricated by mechanical alloying(MA) and spark plasma sintering(SPS).The microstructural evolutions,mechanical properties and strengthening mechanisms of the alloys were systematically investigated.The nanocrystalline mechanically alloyed powders with simple bodycentered cubic(BCC) phase were obtained after 40 h MA process.Afterward,the powders were sintered using SPS in the temperature range from 1500 ℃ to 1700 ℃.The bulk alloys were consisted of submicron scale BCC matrix and face-centered cubic(FCC) precipitation phases.The bulk alloy sintered at 1600℃ had an average grain size of 0.58 μm and an FCC precipitation phase of 0.18 μm,exhibiting outstanding micro-hardness of 542 HV,compressive yield strength of 2208 MPa,fracture strength of 3238 MPa and acceptable plastic strain of 24.9% at room temperature.The enhanced mechanical properties of the MoNbTaTiV RHEA fabricated by MA and SPS were mainly attributed to the grain boundary strengthening and the interstitial solid solution strengthening.It is expectable that the MA and SPS processes are the promising methods to synthesize ultra-fine grains and homogenous microstructural RHEA with excellent mechanical properties.     

Microstructure and property characterization of Al-based composites reinforced with CuZrAl particles fabricated by mechanical alloying and spark plasma sintering

In the present work, CuZrAl metallic glass particles were synthesized by mechanical alloying method. High relative density Al-based composites (ABCs) reinforced with different volume fraction of CuZrAl particles have been fabricated by spark plasma sintering (SPS) technique. The microstructures, mechanical properties and corrosion resistance in seawater solution of the ABCs were investigated. The sintered products are all composed of fcc-Al, Al₃Zr and CuAl₂ phases. For CuZrAl addition, bright and network precipitates are clearly observed in the Al matrix. On account of the interdiffusion of Al and Cu atoms between matrix and reinforcement, the ABCs present the good interfacial bonding. Compared with SPS-ed pure Al bulk, ABCs possess the excellent mechanical properties. It is mainly ascribed to the second phase strengthening, continuously distributed precipitates, high relative density or bonding interface, and grain refinement strengthening. Thereinto, combined with a degree of plastic strain, the composite with 20?vol% CuZrAl reinforcement reveals the best micro-hardness (290?HV), and the highest yield strength and fracture strength of 408 and 459?MPa, respectively. Moreover, the ABCs bear the better pitting resistance with wide passive region in seawater solution.     

机械合金化-放电等离子烧结Al2Cu颗粒增强Al基复合材料的制备

以Al粉和Cu粉为原料,采用机械合金化(MA)和放电等离子烧结(SPS)工艺,原位合成了致密的Al₂Cu/Al块体复合材料,着重研究了MA过程中粉末的形貌、尺寸和物相结构的变化以及SPS后复合材料的微观组织和力学性能。结果表明: 在MA过程中,随着MA时间延长,部分Cu原子逐渐固溶于Al原子晶格中,形成均匀过饱和的固溶体Al(Cu);在SPS过程中,Cu从过饱和固溶体中析出并与Al反应形成Al₂Cu颗粒,且弥散分布于Al基体中,形成Al₂Cu/Al复合材料;Al₂Cu/Al复合材料的致密度高达98.7%,室温下的压缩断裂强度为611.3 MPa,延伸率为9.6%,具有良好的力学性能。     

Processing,spark plasma sintering,and mechanical behavior of alumina/titanium composites

This paper focuses on the study of the processing and mechanical properties, (flaw tolerance and R-curve behavior) of alumina–titanium ceramic–metal composites produced by spark plasma sintering. In order to obtain homogenously dispersed composites, a rheological study was carried out by measuring the flow behavior in different conditions of solid content, amount of dispersant and shear stress. It has been found that, with the suitable conditions (80 wt% solids and 3 wt% deflocculant), a ceramic–metal homogeneously dispersed (Al₂O₃–Ti) composite can be obtained. After sintering, the composites were mechanically tested and the cermet showed an important improvement in the flaw tolerance and R-curve behavior when compared with the monolithic material. It has been demonstrated by scanning electronic microscopy that this improvement is a consequence of the reinforcement mechanisms provided by the metallic particles that interact with the crack producing a notable increase in toughness up to ~8 MPa m^1/2.     

Rapidly sintering nanosized SiC particle reinforced TiC composites by the spark plasma sintering (SPS) technique

Different content of nanosized SiC reinforced TiC matrix composites were fabricated at 1600°C by spark plasma sintering (SPS) without any aids. It was found that the materials could be sintered in a relatively short time (12 min) and low sintering temperature (1600°C) to satisfactory relative density (99%). The phase distribution and microstructure of composites have been investigated by optical microscopy and scanning electron microscope. Fracture toughness and Vickers hardness at room temperature were also measured by indentation tests. The results showed that nanosized SiC particles addition could inhibit the coalescence of TiC grains and increase fracture toughness of composites due to the crack deflections.     

Fabrication and mechanical properties of monolithic MoSi2 by spark plasma sintering

Fine MoSi₂ powders containing a small amount of Mo₅Si₃ have been prepared by self-propagating high-temperature synthesis (SHS), followed by spark plasma sintering (SPS) for 10 min at 1200-1500°C and 30 MPa. Dense MoSi₂ materials, in which the grain size is ∼7.5 μm, have been fabricated at 1300°C. They exhibit excellent mechanical properties: Vicker’s hardness H_v (10.6 GPa), fracture toughness K_IC (4.5 MPa m^1/2), and bending strength σ_b (560 MPa). The strength of 325 MPa can be retained up to 1000°C.