Dielectric properties of spark plasma sintered AlN/SiC composite ceramics

In this study, we have investigated how the dielectric loss tangent and permittivity of AlN ceramics are affected by factors such as powder mixing methods, milling time, sintering temperature, and the addition of a second conductive phase. All ceramic samples were prepared by spark plasma sintering (SPS) under a pressure of 30 MPa. AlN composite ceramics sintered with 30wt%–40wt% SiC at 1600℃ for 5 min exhibited the best dielectric loss tangent, which is greater than 0.3. In addition to AlN and β-SiC, the samples also contained 2H-SiC and Fe₅Si₃, as detected by X-ray difraction (XRD). The relative densities of the sintered ceramics were higher than 93%. Experimental results indicate that nano-SiC has a strong capability of absorbing electromagnetic waves. The dielectric constant and dielectric loss of AlN-SiC ceramics with the same content of SiC decreased as the frequency of electromagnetic waves increased from 1 kHz to 1 MHz.     

放电等离子烧结制备Cu/Ti3SiC2-TiC复合材料

选用单质粉(Ti,Si,C,Al)为原料,采用机械合金化法制备含有Ti3SiC2和TiC的混合粉体,然后将Ti3SiC2,TiC和Cu的混合粉体进行放电等离子烧结,以制备Cu/Ti3SiC2-TiC复合材料,并对其组织耐磨性进行了研究。实验结果表明,放电等离子烧结可制备致密的Cu/Ti3SiC2-TiC复合材料,复合材料的显微硬度随强化相(Ti3SiC2-TiC)掺加量的增加显著提高,当强化相掺加量为20 vol%时,复合材料的硬度值达1.58 GPa。Cu/Ti3SiC2-TiC复合材料的耐磨性随强化相含量增加显著提高,当强化相掺入量为20 vol%时,复合材料的耐磨性为纯Cu的4倍。     

Interfacial behavior of Fe76Si9B10P5/Zn0.5Ni0.5Fe2O4 amorphous soft magnetic composite during spark plasma sintering process

Fe_(76)Si_9B_(10)P_5/Zn_(0.5)Ni_(0.5)Fe_2O_4 amorphous composite with micro-cellular structure and high electrical resistivity was prepared by spark plasma sintering(SPS) at 487 °C. XRD and SEM results showed that the Fe_(76)Si_9B_(10)P_5 alloy powders remained the amorphous state and the composite was dense. A fusion zone at interface of Fe_(76)Si_9B_(10)P_5 cell body and Zn_(0.5)Ni_(0.5)Fe_2O_4 cell wall was observed by TEM, which also indicates the formation of local high temperature. The interface bonding based on the formation of local high temperature in SPS process was observed. It is believed that the tip effect of Zn_(0.5)Ni_(0.5)Fe_2O_4 nanoparticles promotes the local discharging and plasmas creation in the gaps, and the discharging energy forms an instantaneous local high temperature to complete the local sintering and the densification of Zn_(0.5)Ni_(0.5)Fe_2O_4 particles at a low nominal sinter temperature. Simultaneously, the local high temperature stimulates the adjacent gaps discharging, thus facilitate the continuous formation of new discharging path. Finally, sintering and densification of the amorphous composite is complete.     

Effect of spark plasma sintering and reinforcements on the formation of ultra-fine and nanograins in AA2024-TiB2-Y hybrid composites

This study reports the influence of sintering mechanism and reinforcement materials on the formation of ultra-fine and nanograins in Al-TiB₂-Y nanohybrid composites. The mechanical properties of the composites and their corresponding micro and nanostructures are correlated. The experimental and characterization results revealed that despite the addition of TiB₂, the hard and brittle Al₃Ti phase formation in the composites was suppressed and hence, their ductility was retained. It was found that yttrium content of 0.3 ?wt% was the optimum amount which created advantageous spark plasma sintering conditions, and the addition of 0.3 ?wt% promoted the formation of bi-modal size grains (ultra-fine and nano) along with micro grains, Ω and other nano precipitates, resulting in a significant enhancement in the composite properties. The formation of ultra-fine and nanograins may be attributed to the combined effect of melting and rapid solidification at necking zones due to Joule's heating and thermo-mechanical fatigue. Among all the sintered composites, the highest hardness (137 HV), ultimate tensile strength (UTS) (496 ?MPa), yield strength (YS) (438 ?MPa) with 15.7% elongation were obtained in the sintered sample reinforced with 1.0 ?wt% TiB₂ and 0.3 ?wt% yttrium.     

Effect of sintering temperature on phase evolution of Al_(86)Ni_6Y_(4.5)Co_2La_(1.5) bulk amorphous composites synthesized via mechanical alloying and spark plasma sintering

Al_(86)Ni_6Y_(4.5)Co_2La_(1.5) amorphous powders were synthesized by mechanical alloying for 200 h. Subsequent consolidation was performed via spark plasma sintering in the temperature range of 250 ℃ to 500 ℃ at the pressure of 500 MPa. The role of viscous flow on densification was investigated by studying the viscosity change of the amorphous phase at different consolidation temperatures. The decrease in viscosity at higher sintering temperatures resulted in better particle bonding and densification of consolidated samples. The formation of only FCC Al was observed in the consolidated samples at sintering temperatures ≤ 300 ℃ and the intermetallic phases formed at temperatures ≥ 400 ℃. The mechanical properties of the bulk samples were measured by Vickers microhardness and nanoindentation tests. The testing results showed that the average values of microhardness, nanohardness and elastic modulus of the sample consolidated at 500 ℃ were 3.06 ± 0.14 GPa,4.85 ± 1.14 GPa and 89.53 ± 9.25 GPa, respectively. The increase in hardness and elastic modulus of the higher temperature consolidated samples is attributed to the improvement in particle bonding, densification and distribution of various hard intermetallic phases in the amorphous matrix.     

Effect of sintering temperature on the preparation of Cu–Ti3SiC2 metal matrix composite

Ti3SiC2 has the potential to replace graphite as reinforcing particles in Cu matrix composites for applications in brush,electrical contacts and electrode materials.In this paper the fabrication of Cu-Ti3SiC2 metal matrix composites prepared by warm compaction powder metallurgy forming and spark plasma sintering(SPS) was studied.The stability of Ti3SiC2 at different sintering temperatures was also studied.The present experimental results indicate that the reinforcing particles in Cu-Ti3SiC2 composites are not stable at and above 800℃.The decomposition of Ti3SiC2 will lead to the formation of TiC and/or other carbides and TiSi2.If purity is the major concern,the processing and servicing temperatures of the Cu-Ti3SiC2 composite should be limited to 750℃ or lower.The composites prepared by warm compaction forming and SPS sintering at 750℃ have lower density when compared with the composites prepared by SPS sintering at 950℃,but their electrical resistivity values are very close to each other and even lower.     

Microstructure and mechanical properties of Cr doped WCoB based cermets by spark plasma sintering and first principle calculation

WCoB based cermet is a potential hard alloy to replace WC-Co cermets with high hardness and corrosion resistance. WCoB based cermets with different Cr doping contents were fabricated by spark plasma sintering in liquid phase sintering stage. The densification behavior, phase composition, microstructure and mechanical properties of Cr doped WCoB cermets were investigated by XRD, EDS and SEM. Due to the lower density of Cr,the density of WCoB cermets decreased with the increasing of Cr doping content. The phase composition consisted of Cr doped WCoB, unreacted W, Co–Cr binary binder phase. When the doping content exceeded11.736 wt%, the Cr enrichment zones appeared, which was harmful to the TRS. The increasing of Cr doping content contributed to the increase of unreacted W phases content and the formation of pores. The maximum value of Vickers hardness was 1751 Hv0.5 at 9.356 wt% Cr doping content. The variation trend was explained by first principle calculation, which is consistent with Hv-Zhou hardness model.     

放电等离子烧结微胞结构复合材料有限元模拟

采用ANSYS软件建立三维热‐电耦合瞬态有限元模型,对微胞结构复合材料的放电等离子烧结过程进行模拟。模拟计算结果表明,烧结低温阶段石墨模具向样品传热,烧结过程类似于热压烧结,烧结高温阶段样品自发热,样品附近沿径向形成温度梯度。     

放电等离子烧结制备碳化钛块材研究

利用放电等离子烧结(SPS)对碳化钛(TiC)/氢化钛(TiH2)混合粉末进行烧结以制备块材。利用X射线衍射(XRD)并结合Rietveld精修法对块材进行定性与结构分析;借助扫描电子显微镜(SEM)对块材断面微观形貌进行观察;测试了块材硬度并探讨SPS技术制备TiC块材的致密化过程与反应机理。结果表明:混合粉末经SPS烧结,获得了高度致密的TiC块材;与传统烧结方法比较,SPS技术更具低温快速性。     

激光烧结纳米Al_2O_3微观结构研究

利用电子扫描电镜(SEM)和X射线衍射仪(XRD)对激光烧结纳米Al2O3粉末块体材料进行了试验分析与研究.结果表明,纳米晶粒的微观结构在烧结过程中不断地发生变化,但激光烧结基本可以抑制纳米晶粒的生长,得到具有纳米尺度的烧结材料.     

Influence of sintering temperature on the thermoelectric properties of Ba8Ga16Si30 clathrate treated by spark plasma sintering

A series of Ba8Ga16Si30 clathrate samples were prepared by arc melting, ball milling, acid washing, and spark plasma sintering (SPS). X-ray diffraction analysis revealed that the lattice of the Ba8Ga16Si30 samples expanded as the SPS temperature was increased from 400 to 750°C. Lattice contraction recurred when the SPS temperature was further increased in the range of 750–1000°C. This phenomenon can be explained by the variation of Ga content in the lattice. The thermoelectric figure of the merit ZT value of clathrates increased with the increase in SPS temperature and reached a maximum when the sample was subjected to SPS at 800°C. A further increase in SPS temperature did not contribute to the improvement of ZT. The variation of the lattice parameter a vs. SPS temperature T was similar to the variation ob-served in the ZT–T curve.     

放电等离子烧结热变形Nd-Fe-B磁体的磁性能研究

采用放电等离子烧结技术,利用不同速率的快淬薄带制备出各向异性的热变形Nd-Fe-B磁体,运用振动样品磁强计和扫描电子显微镜对热变形磁体的磁性能和微观结构进行研究.结果表明：随着快淬薄带速率的增加,获得最佳磁性能的热变形温度也逐渐增加,三类热变形Nd-Fe-B磁体获得最佳磁性能的热变形温度分别为650,680和700°C;磁体最佳磁性能中的剩磁和最大磁能积随着快淬薄带速率的增加而降低,而内禀矫顽力却略有增加.磁体的晶粒尺寸随着热变形温度的增加而增大;相同热变形温度下,磁体的晶粒尺寸随快淬速率的增加而减小.     

放电等离子烧结Al20Cr20Fe25Ni25Mn10高熵合金的硬度和腐蚀性能研究

采用放电等离子烧结(SPS)技术在不同温度（800、900和200°C）下保温不同时间（4、8和12 min）合成了Al₂₀Cr₂₀Fe₂₅Ni₂₅Mn₁₀高熵合金（HEA）。通过扫描电子显微镜、能谱仪（EDS）、维氏显微硬度计、极化曲线等对合金的微观结构、显微硬度和腐蚀进行了实验研究。X-射线衍射（XRD）表征了所制备合金的成分。EDS结果显示不论烧结参数如何变化,合金均由原始合金元素组成。XRD、EDS和扫描电子显微镜的结果说明所制备的合金具有球形微观结构,呈现出面心立方结构相,这是基于固溶机制形成的。这表明SPS合金具有HEAs的特征。在1000°C保温 12 min生产的合金显微硬度最高,为HV 447.97,热处理后其硬度降至HV 329.47。同一合金表现出优异的耐腐蚀性能。烧结温度升高,Al₂₀Cr₂₀Fe₂₅Ni₂₅Mn₁₀合金可具有更高的密度、显微硬度和耐腐蚀性。     

Effects of AlN on the densification and mechanical properties of pressureless-sintered SiC ceramics

In the present work, Si C ceramics was fabricated with Al N using B_4 C and C as sintering aids by a solid-state pressureless-sintered method. The effects of Al N contents on the densification, mechanical properties, phase compositions, and microstructure evolutions of as-obtained Si C ceramics were thoroughly investigated. Al N was found to promote further densification of the Si C ceramics due to its evaporation over 1800 °C,transportation, and solidification in the pores resulted from Si C grain coarsening. The highest relative density of 99.65% was achieved for Si C sample with 15.0 wt% Al N by the pressureless-sintered method at 2130 °C for 1 h in Ar atmosphere. Furthermore, the fracture mechanism for Si C ceramics containing Al N tended to transfer from single transgranular fracture mode to both transgranular fracture and intergranular fracture modes when the sample with 30.0 wt% Al N sintered at 1900 °C for 1 h in Ar. Also, Si C ceramics with 30.0 wt% Al N exhibited the highest fracture toughness of 5.23 MPa m~(1/2) when sintered at 1900 °C.     

Effect of sintering on the relative density of Cr-coated diamond/Cu composites prepared by spark plasma sintering

Cr-coated diamond/Cu composites were prepared by spark plasma sintering. The effects of sintering pressure, sintering temperature, sintering duration, and Cu powder particle size on the relative density and thermal conductivity of the composites were investigated in this paper. The influence of these parameters on the properties and microstructures of the composites was also discussed. The results show that the relative density of Cr-coated diamond/Cu reaches ~100% when the composite is gradually compressed to 30 MPa during the heating process. The densification temperature increases from 880 to 915℃ when the diamond content is increased from 45vol% to 60vol%. The densification temperature does not increase further when the content reaches 65vol%. Cu powder particles in larger size are beneficial for increasing the relative density of the composite.     

SPS烧结温度对93W-4.9Ni-2.1Fe合金微观结构及性能的影响

以高能球磨法制备的93W-4.9Ni-2.1Fe复合粉末为原料,采用放电等离子烧结技术制备93W--4.9Ni-2.1Fe合金,研究了烧结温度对钨合金微观组织及性能的影响.采用扫描电镜对试样的断口进行观察,采用能量色散谱仪对合金的组元进行成分分析.结果表明:①烧结温度对合金的性能有显著的影响,在1 350℃时钨合金的抗拉强度达到一个极大值,为981 MPa,此时钨合金的相对密度和W晶粒的尺寸分别为98.9%和5μm;②当烧结温度达到1375℃时,合金中Ni元素开始挥发,随着温度的快速上升,合金中Ni元素的挥发不断加剧,当烧结温度升高至1425℃时合金中Ni元素已完全挥发;③合金的断裂方式随着烧结温度的升高发生显著的变化,当烧结温度升至1350℃时钨合金的断裂方式由W晶粒界面分离向W-W、W-黏结相界面断裂转变,而当烧结温度超过此温度时钨合金的断裂方式又转变为W晶粒的沿晶脆性断裂;④SPS快速烧结能够有效抑制W晶粒的长大,促进钨合金的细晶强化作用.     

Microstructural evolution and mechanical properties of Nb-Si-Cr ternary alloys with a tri-phase Nb/Nb5Si3/Cr2Nb microstructure fabricated by spark plasma sintering

In this work, pure Nb, Nb₅Si₃ and Laves Cr₂Nb compound powders were used as raw materials to prepare Nb-Si-Cr ternary alloys by spark plasma sintering (SPS). A comprehensive estimation of the microstructure and properties, including room temperature fracture toughness, high temperature strength and oxidation resistance, of the Nb-Si-Cr ternary alloys as a function of the Nb/Nb₅Si₃/Cr₂Nb phase volume fraction combinations was conducted. The results showed that Nb-Si-Cr ternary samples with the relative density larger than 98.42% were obtained by SPS processing, and the samples all consisted of Nb, Nb₅Si₃ and Cr₂Nb phases that were distributed homogeneously. The fracture toughness K_Q of the Nb/Nb₅Si₃/Cr₂Nb microstructure, which was dominated by the Nb phase, naturally increased with the Nb fraction. As expected, the room-temperature Vickers hardness and the high-temperature strength of the bulk alloys increased monotonically with the increasing of the stiffening Nb₅Si₃ fraction. Interestingly, the binary Cr₂Nb phase played a positive role in the high temperature strength and oxidation resistance. Finally, the fracture modes of the typical Nb/Nb₅Si₃/Cr₂Nb microstructures under bending and compression conditions at room and high temperatures as well as the oxidation mechanism are described and discussed.     

微胞结构复合材料界面的TEM研究

利用TEM研究了通过放电等离子烧结（Spark Plasma Sintering,SPS）方法制备的AlMnCe/Al2O3微胞结构金属/陶瓷纳米复合材料界面的微观结构。结果表明,Al2O3纳米粉末在放电局域高温作用下形成了胞壁烧结体相,纳米Al2O3胞壁层与AlMnCe胞体合金之间有70 nm的熔渗过渡区,界面结合良好。纳米Al2O3胞壁层的烧结暗示SPS烧结条件下的温度分布具有明显的微观局域性差异,界面处有放电引起的短时高温经历。     

高温SiC/Al2O3复合抗氧化涂层性能的研究

本文通过SiC及SiC/Al2O3复合涂层抗氧化性能的研究，认为采用高温浸渗工艺，在石墨制品表面形成的SiC涂层与基体有合理的界面结构，该涂层能对石墨制品起到良好的抗氧化防护作用。而SiC/Al2O3复合涂层使石墨制品具有更佳的抗氧化能力。     

Cu／Ti3AlC2复合材料的耐磨性研究

以元素单质粉Ti,Al,C,Cu为原料,采用机械合金化和放电等离子烧结（SPS）,成功制备了Cu／Ti3AlC2复合材料块体,并对其进行了组织性能分析。实验结果表明：采用SPS烧结技术制备的Cu／Ti3AlC2复合材料,随着Ti3AlC2含量的增加,其显微硬度逐渐提高,相同烧结工艺条件下（900℃烧结,保温20min）添加15vol％Ti3AlC2复合材料的硬度比纯Cu提高近2倍;添加适量的Ti3AlC2可显著提高复合材料的耐磨性,当复合材料中含5vol％Ti3AlC2时,磨损量降低30％以上。