Microstructure and mechanical properties of Nb–Si alloys fabricated by spark plasma sintering

This paper deals with microstructural evolutions and mechanical properties of Nb-Si binaries containing dual-phase Nb/Nb5Si3 with Nb to Nb5Si3 fraction ratios of 90:10,80:20,70:30 and 50:50,prepared by spark plasma sintering(SPS).Dense Nb/Nb5Si3 samples with a relative density larger than 99.5% were obtained by SPS processing.The SPS samples consist of the Nb and Nb5Si3 phases with less than 3% fraction of NbO oxide.Hv at room temperature,and compressive strength at 1150℃ and 1250 1C of the bulk SPS alloys increase monolithically by enhancing fraction of the stiffening Nb5Si3 phase.For example,0.2% yield strength,σ0.2,increases from 175 MPa to 420 MPa at 1150℃ and from 110 MPa to 280 MPa at 1250℃,when the Nb5Si3 fraction increases from 10% to 50%.It is interesting that the fracture toughness,KQ,of the bulk SPS samples seems not to be sensitive to phase fraction.Heat treatment,however,plays a key role on the KQ as compared with that of the as-sintered state,at the corresponding Nb5Si3 fraction and considerably improves the KQ by about 100% for samples with the Nb5Si3 fractions of 10%-30%,and by about 50% for the sample with 50% Nb5Si3 fraction.     

放电等离子烧结合成TiC/TiB_2颗粒增强的超细晶钛基复合材料

采用放电等离子烧结技术结合非晶晶化法制备了不同体积分数的TiC/TiB2颗粒增强的超细晶钛基复合材料.运用X射线衍射分析、扫描电子显微镜和万能材料试验机等实验手段,对合成的超细晶钛基复合材料进行测试分析.结果表明：随着外加TiC/TiB2颗粒的增加,钛基复合材料试样的致密度逐渐降低.TiC颗粒与基体不发生反应,而TiB2颗粒的加入改变了TiB2颗粒与基体界面的组织形貌,但对远离界面处的基体组织形貌没有影响,其组织均由-Ti（Nb）相和（Cu,Ni）-Ti2相组成,且-Ti（Nb）相连续分布.同时,TiC颗粒的增强效果优于TiB2颗粒,35vol.%（体积分数）TiC颗粒增强的复合材料试样的断裂强度最高,达2209MPa.     

Microstructure,thermal properties,and corrosion behaviors of FeSiBAlNi alloy fabricated by mechanical alloying and spark plasma sintering

An equiatomic FeSiBAlNi amorphous high-entropy alloy (HEA) was fabricated by mechanical alloying (MA). A fully amorphous phase was obtained in the FeSiBAlNi HEA after 240 h of MA. The bulk FeSiBAlNi samples were sintered by spark plasma sintering (SPS) at 520 and 1080℃ under a pressure of 80 MPa. The sample sintered at 520℃ exhibited an amorphous composite structure comprising solid-solution phases (body-centered cubic (bcc) and face-centered cubic (fcc) phases). When the as-milled amorphous HEA was consolidated at 1080℃, another fcc phase appeared and the amorphous phase disappeared. The sample sintered by SPS at 1080℃ exhibited a slightly higher melting temperature compared with those of the as-milled alloy and the bulk sample sintered at 520℃. The corrosion behaviors of the as-sintered samples were investigated by potentiodynamic polarization measurements and immersion tests in seawater solution. The results showed that the HEA obtained by SPS at 1080℃ exhibited better corrosion resistance than that obtained by SPS at 520℃.     

Graphene-reinforced aluminum matrix composites prepared by spark plasma sintering

Graphene-reinforced 7055 aluminum alloy composites with different contents of graphene were prepared by spark plasma sintering (SPS). The structure and mechanical properties of the composites were investigated. Testing results show that the hardness, compressive strength, and yield strength of the composites are improved with the addition of 1wt% graphene. A clean, strong interface is formed between the metal matrix and graphene via metallurgical bonding on atomic scale. Harmful aluminum carbide (Al₄C₃) is not formed during SPS processing. Further addition of graphene (above 1wt%) results in the deterioration in mechanical properties of the composites. The agglomeration of graphene plates is exacerbated with increasing graphene content, which is the main reason for this deterioration.     

Investigation on microstructural, mechanical and electrochemical properties of aluminum composites reinforced with graphene nanoplatelets

In present study, the microstructure, mechanical and electrochemical properties of aluminum–graphene nanoplatelets (GNPs) composites were investigated before and after extrusion. The contents of graphene nanoplatelets (GNPs) were varied from 0.25 to 1.0 wt.% in aluminum matrix. The composites were fabricated thorough powder metallurgy method, and the experimental results revealed that Al-0.25%GNPs composite showed better mechanical properties compared with pure Al, Al-0.50%GNPs and Al-0.1.0%GNPs composites. Before extrusion, the Al-0.25%GNPs composite showed ~13.5% improvement in ultimate tensile strength (UTS) and ~50% enhancement in failure strain over monolithic matrix. On the other hand, Al-0.50%GNPs and Al-0.1.0%GNPs composites showed the tensile strength lower than monolithic matrix. No significant change was observed in 0.2% yield strength (YS) of the composites. However, the extruded materials showed different trends. The 0.2%YS of composites increased with increase in GNPs filler weight fractions. Surprisingly, UTS of composites with 0.25 and 0.50% GNPs was lower than monolithic matrix. The failure strain of the baseline matrix was enhanced by ~46% with 0.25% graphene nanoplatelets. The superior mechanical properties (in terms of failure strain) of the Al-0.25%GNPs composite maybe attributed to 2-D structure, high surface area and curled nature of graphene. In addition, the corrosion resistance of pure Al and its composites reinforced with 0.5 and 1.0 wt% GNPs was also investigated. It was found that the corrosion rate increased considerably by the presence of GNPs.     

High-temperature mechanical properties and deformation behavior of high Nb containing TiAl alloys fabricated by spark plasma sintering

A high Nb containing TiAl alloy was prepared from the pre-alloyed powder of Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y (at%) by spark plasma sintering (SPS). Its high-temperature mechanical properties and compressive deformation behavior were investigated in a temperature range of 700 to 1050℃ and a strain rate range of 0.002 to 0.2 s-1. The results show that the high-temperature mechanical properties of the high Nb containing TiAl alloy are sensitive to deformation temperature and strain rate, and the sensitivity to strain rate tends to rise with the deformation temperature increasing. The hot workability of the alloy is good at temperatures higher than 900℃, while fracture occurs at lower temperatures. The flow curves of the samples compressed at or above 900℃ exhibit obvious flow softening after the peak stress. Under the deformation condition of 900-1050℃ and 0.002-0.2 s-1, the interrelations of peak flow stress, strain rate, and deformation temperature follow the Arrhenius' equation modified by a hyperbolic sine function with a stress exponent of 5.99 and an apparent activation energy of 441.2 kJ·mol-1.     

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.     

放电等离子烧结TiAl基合金的显微组织及力学性能

以Ti-47.5Al-2.5V-1.0Cr合金粉末为原料,采用放电等离子烧结工艺制备出TiAl基合金,并研究了制备工艺、显微组织与室温力学性能三者的关系.结果表明,采用放电等离子烧结方法可制备出致密度高、组织均匀的TiAl基合金.烧结温度对合金的显微组织影响显著,且其室温力学性能与显微组织密切相关,显微组织越细小,室温强度和塑性越高.当烧结温度为1100℃时,制备出的TiAl-V-Cr合金显微组织类型为细小双态组织,具有35.2%的压缩率和3321MPa的断裂强度,显示出较好的室温压缩性能.     

Mechanical properties and friction behaviors of CNT/AlSi10Mg composites produced by spark plasma sintering

The mechanical properties and friction behaviors of CNT/AlSi10Mg composites produced by spark plasma sintering (SPS) were investigated.The results showed that the densities of the sintered composites gradually increased with increasing sintering temperature and that the highest microhardness and compressive strength were achieved in the specimen sintered at 450℃.CNTs dispersed uniformly in the AlSi10Mg matrix when the addition of CNTs was less than 1.5wt％.However,when the addition of CNTs exceeded 1.5wt％,the aggregation of CNTs was clearly observed.Moreover,the mechanical properties (including the densities,compressive strength,and microhardness) of the composites changed with CNT content and reached a maximum value when the CNT content was 1.5wt％.Meanwhile,the minimum average friction coefficient and wear rate of the CNT/AlSi10Mg composites were obtained with 1.0wt％ CNTs.     

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。     

放电等离子烧结制备Al-Zn-Mg-Cu纳米晶合金的组织

利用低温液氮球磨和放电等离子烧结工艺制备了块体纳米晶Al-Zn-Mg-Cu合金.采用X射线衍射(XRD)技术分析了材料的晶粒尺寸和微观应变,利用透射电镜(TEM)研究了合金微观组织的演变.结果表明:采用放电等离子烧结法制备的7000系纳米铝合金具有两种不同的纳米晶结构,以晶粒尺寸50～100nm的等轴晶为主,少量200～400nm的大晶粒为辅;烧结过程中发生再结晶及第二相析出,析出的第二相以η(MgZn2)为主,θ(Al2Cu)以及S(Al2CuMg))为辐.     

Mechanical properties and friction behaviors of CNT/AlSi_(10)Mg composites produced by spark plasma sintering

The mechanical properties and friction behaviors of CNT/AlSi_(10)Mg composites produced by spark plasma sintering(SPS) were investigated.The results showed that the densities of the sintered composites gradually increased with increasing sintering temperature and that the highest microhardness and compressive strength were achieved in the specimen sintered at 450°C.CNTs dispersed uniformly in the AlSi_(10)Mg matrix when the addition of CNTs was less than 1.5wt%.However,when the addition of CNTs exceeded 1.5wt%,the aggregation of CNTs was clearly observed.Moreover,the mechanical properties(including the densities,compressive strength,and microhardness) of the composites changed with CNT content and reached a maximum value when the CNT content was 1.5wt%.Meanwhile,the minimum average friction coefficient and wear rate of the CNT/AlSi_(10)Mg composites were obtained with 1.0wt% CNTs.     

石墨烯增强MC尼龙复合材料的力学和摩擦学性能

采用原位聚合法制备了石墨烯/MC尼龙(MCPA)复合材料。使用X射线衍射仪(XRD)和傅立叶红外光谱仪(FT-IR)对石墨烯的结构进行表征,研究了石墨烯含量对复合材料的力学和摩擦学性能的影响。研究结果表明,添加0.05%的石墨烯可以使MC尼龙复合材料的拉伸强度、弹性模量、弯曲强度和弯曲模量分别提高了17.4%,14.7%,17.5%,24.3%;在干摩擦条件下,将石墨烯添加到MC尼龙中,能显著降低复合材料的磨损量,但复合材料的摩擦系数变化不明显;随着石墨烯含量的增加,石墨烯/MC尼龙复合材料的磨损机理由粘着磨损转变成疲劳磨损。     

Sintering behavior and thermal conductivity of nickel-coated graphite flake/copper composites fabricated by spark plasma sintering

Nickel-coated graphite flakes/copper (GN/Cu) composites were fabricated by spark plasma sintering with the surface of graphite flakes (GFs) being modified by Ni-P electroless plating. The effects of the phase transition of the amorphous Ni-P plating and of Ni diffusion into the Cu matrix on the densification behavior, interfacial microstructure, and thermal conductivity (TC) of the GN/Cu composites were systematically investigated. The introduction of Ni-P electroless plating efficiently reduced the densification temperature of uncoated GF/Cu composites from 850 to 650℃ and slightly increased the TC of the X-Y basal plane of the GF/Cu composites with 20vol%-30vol% graphite flakes. However, when the graphite flake content was greater than 30vol%, the TC of the GF/Cu composites decreased with the introduction of Ni-P plating as a result of the combined effect of the improved heat-transfer interface with the transition layer, P generated at the interface, and the diffusion of Ni into the matrix. Given the effect of the Ni content on the TC of the Cu matrix and on the interface thermal resistance, a modified effective medium approximation model was used to predict the TC of the prepared GF/Cu composites.     

Surfactant-decorated graphite nanoplatelets(GNPs) reinforced aluminum nanocomposites: sintering effects on hardness and wear

The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was addressed by sonication and non-covalent surface functionalization of graphite nanoplatelets(GNPs) using two types of surfactant: anionic(sodium dodecyl benzene sulfate(SDBS)) and non-ionic polymeric(ethyl cellulose(EC)). After colloidal mixing with Al powder, consolidation was performed at two sintering temperatures(550 and 620°C). The structure, density, mechanical and wear properties of the nanocomposite samples were investigated and compared with a pure Al and a pure GNPs/Al nanocomposite sample. Noticeably, EC-based 0.5 wt% GNPs/Al samples showed the highest increment of 31% increase in hardness with reduced wear rate of 98.25% at 620°C, while a 22% increase in hardness with reduced wear rate of 96.98% at 550°C was observed, as compared to pure Al. Microstructural analysis and the overall results validate the use of EC-based GNPs/Al nanocomposites as they performed better than pure Al and pure GNPs/Al nanocomposite at both sintering temperatures.     

Surfactant-decorated graphite nanoplatelets (GNPs) reinforced aluminum nanocomposites: sintering effects on hardness and wear

The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was addressed by sonication and non-covalent surface functionalization of graphite nanoplatelets (GNPs) using two types of surfactant: anionic (sodium dodecyl benzene sulfate (SDBS)) and non-ionic polymeric (ethyl cellulose (EC)). After colloidal mixing with Al powder, consolidation was performed at two sintering temperatures (550 and 620℃). The structure, density, mechanical and wear properties of the nanocomposite samples were investigated and compared with a pure Al and a pure GNPs/Al nanocomposite sample. Noticeably, EC-based 0.5wt% GNPs/Al samples showed the highest increment of 31% increase in hardness with reduced wear rate of 98.25% at 620℃, while a 22% increase in hardness with reduced wear rate of 96.98% at 550℃ was observed, as compared to pure Al. Microstructural analysis and the overall results validate the use of EC-based GNPs/Al nanocomposites as they performed better than pure Al and pure GNPs/Al nanocomposite at both sintering temperatures.     

Structural and mechanical properties of 7075 alloy strips fabricated by roll-casting in a static magnetic field

The influences of a 0.2 T static magnetic field on the microstructure of 7075 aluminum alloys sheets produced with a twin-roll continuous caster at 675°C were investigated in this paper. Under a uniform magnetic field, the primary dendrites were refined and tended to be equiaxed. The microstructure consisted of an intermediate case between dendritic and equiaxed grains. Moreover, the use of an external static field in the twin-roll casting process can reduce heat discharge, resulting in a decrease in undercooling, and may also account for the abatement of segregation bands. In addition, the static magnetic field effectively improved the solute mixing capacity, and the added atoms more easily diffused from precipitates to the α-Al matrix, which resulted in an increase in the mechanical properties of the rolled sheets. Specimens prepared both in the presence of a static magnetic field and in the absence of a static magnetic field exhibited brittle-fracture characteristics.     

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.     

Corrosion behaviors of NdFeB magnets prepared by spark plasma sintering

The spark plasma sintering (SPS) technique was introduced into the field of NdFeB preparation due to its own advantages.High property NdFeB magnets with fine grains were prepared by SPS method. The corrosion behaviors of SPS NdFeB were studied by electrochemical measurements and 92% RH hyther tests at 353 K. The results were compared with those of the traditional sintered NdFeB magnets. It shows that both the SPS NdFeB and the traditional sintered NdFeB have good corrosion resistance in alkaline environment due to surface passivation; while, the fine grain microstructure of SPS NdFeB results in a more homogeneous phase composition distribution and thus reduces the electrochemical inhomogenity between the ferromagnetic phase and the Nd-rich intergranular phase in the magnet. Therefore, the SPS NdFeB exhibits better corrosion resistance than the traditional sintered NdFeB in neutral and weak acidic environment.     

SPS方法制备铜/金刚石复合材料

采用放电等离子烧结(SPS)方法制备出高体积分数的铜/金刚石复合材料,并对复合材料的致密度、热导率和热膨胀系数等进行了研究.结果表明,采用该方法制备的铜/金刚石复合材料微观组织均匀,致密度分布为94%～99%,最高热导率为305W.(m.K)-1,热膨胀系数与常见电子半导体材料相匹配,能够满足电子封装材料的要求.