W-30Cu纳米复合粉末液相烧结致密化与晶粒长大机制

采用喷雾干燥-煅烧、还原工艺制备超细W-30Cu复合粉末,将粉末模压成形,在1340～1420℃液相烧结15～120min,研究其致密化行为及晶粒长大机制。结果表明:W-30Cu复合粉末在液相烧结早期发生了显著的致密化,1340℃烧结15 min致密度可达到90%以上;随烧结时间的延长致密度增加,1380℃烧结90 min相对密度达到99.1%。液相烧结过程中,W晶粒不断长大并逐渐球化,且其晶粒大小G与烧结时间t符合G3∝kt关系,服从液相烧结溶解-析出机制。烧结温度对W晶粒长大影响显著,当温度从1340℃上升到1420℃时,其晶粒长大动力学系数从1.61×10-2μm3/min增大到4.65×10-2μm3/min,液相的形成、颗粒重排、溶解-析出及W晶粒长大使细晶W-Cu获得近全致密。     

超细/纳米W-20Cu复合粉末的液相烧结机制

采用溶胶-喷雾干燥及氢还原工艺制备超细/纳米W-20 Cu复合粉末:将粉末压制成形,在1 340～1 420℃烧结5～180 min,并研究其致密化行为及晶粒长大机制.结果表明:烧结温度对液相烧结致密化起主要作用,W-20Cu复合粉末在液相烧结早期发生了显著的致密化,在1 420℃烧结5 min时,致密度可达到89％以上;随烧结时间的延长,致密度增加,在1 420℃烧结90 min时,相对密度最高,达到99.1％.液相烧结时,W晶粒不断长大并逐渐球化,且其晶粒大小G与时间烧结t符合G3＝G30+kt关系,服从溶解-析出机制.烧结温度对W晶粒长大影响显著,当温度从1 340℃上升到1 420℃时,其晶粒长大动力学系数从1.59×10-2 μm3/min增大到2.47×10-2 μm3/min,这说明液相的形成、颗粒重排、溶解-析出及W晶粒长大使得细晶W-Cu坯体获得近全致密.     

纳米晶W-Cu复合粉末烧结行为

研究了机械合金化制备的纳米晶W-xCu(x=15,20,25)复合粉末的烧结行为.结果表明,纳米晶W-Cu复合粉末烧结致密化强烈地依赖于烧结温度与烧结时间.当烧结温度从1 150℃提高到1 200℃时,烧结30min后的烧结体相对密度由91%～94%增加到97%～98%;当烧结温度超过1 300℃时,烧结体发生快速致密化,5 min内相对密度即可达到98%左右.研究还发现,W-Cu合金中W晶粒尺寸也强烈地依赖于烧结温度,即烧结温度愈高,W晶粒长大愈显著.当压坯在1 200～1 250℃烧结30 min后,所得到的晶粒度约为300～500 nm,其中经1 200℃烧结时的晶粒尺寸约为300～350 nm.另外,Cu含量增加有利于烧结致密化,并降低W晶粒长大的趋势.     

纳米晶WC-10Co复合粉末的烧结致密化行为

研究了机械合金化纳米晶WC-10Co复合粉末的真空烧结致密化行为和一般规律.结果表明:烧结温度的提高和烧结时间的延长有利于样品的烧结致密化过程,在1 275～1 300℃致密化速度快,在1 300℃,15 min左右致密化过程已基本完成;VC、Cr3C2等复合晶粒长大抑制剂含量的增加不利于致密化过程;新型晶粒长大抑制剂A可以更有效地阻碍晶粒长大;纳米晶WC-10Co-0.8VC/Cr3C2-0.2A复合粉末压坯在1375℃,30min烧结条件下,所得的密度为14.48 g/cm3,晶粒尺寸约为180 nm.     

放电等离子烧结温度对超细晶W-40Cu复合材料的影响

采用高能球磨法制备了W-40Cu超细晶复合粉体,继而进行了放电等离子烧结(SPS),获得了致密的超细晶W-40Cu块体复合材料,着重研究了烧结温度对复合材料组织和性能的影响.结果表明,随着烧结温度升高,材料的致密度、硬度和电导率也随之升高;在950℃烧结5 min的W-40Cu复合材料,W颗粒尺寸约300～500 nm,相对致密度达98％,显微硬度HV为287,电导率为17.9 MS/m.     

纳米晶Mo-Cu复合粉末烧结行为的研究

采用溶胶-喷雾干燥-煅烧-氢气还原的方法制备了纳米晶Mo-18Cu、Mo-30Cu、Mo-40Cu复合粉末,研究了纳米晶Mo-Cu粉末的烧结行为以及Cu含量对致密化的影响.结果表明,纳米晶Mo-Cu复合粉末致密化程度高,速度快,在1050～1200 ℃烧结,Mo-30Cu和Mo-40Cu的相对密度可达98%以上,且合金晶粒细小,而Mo-18Cu在1350 ℃以上烧结,相对密度也可达98%以上,但晶粒聚集长大到5 μm左右.研究发现Mo-Cu复合粉末形成了亚稳态的超饱和Mo(Cu)固溶体,随着烧结温度的升高,Cu相逐渐从亚稳态的超饱和Mo(Cu)固溶体颗粒中析出.     

放电等离子烧结制备超细WC基硬质合金

采用纳米碳化钒(V8C7)粉末作为晶粒抑制剂及放电等离子烧结(SPS)方式制备超细WC基硬质合金.X射线衍射结果表明:超细WC基硬质合金主要由WC和Co3C两相组成,随着温度的升高,WC的衍射峰逐渐向小角度偏移.扫描电镜结果表明:SPS和纳米V8C7粉末对超细WC基硬质合金的微观组织具有重要影响.SPS使超细WC基硬质合金在较低温度下(1200℃)实现致密化;纳米V8C7粉末可以有效抑制超细WC基硬质合金中WC的晶粒长大,1200℃时WC的晶粒尺寸约500 nm.力学性能结果表明:1200℃时超细WC基硬质合金具有较高的性能(相对密度99.5%,洛氏硬度93.2,断裂韧性12.5 MPa·m1/2).     

高能球磨法制备Fe-C超细晶/纳米晶粉末的研究

采用高能球磨法制备出了平均颗粒尺寸为纳米级的超细Fe-C粉末。利用SEM、XRD等分析手段研究了球磨时间和转速对Fe-C超细晶/纳米晶粉末颗粒形貌、尺寸和合金化效果的影响。结果表明,Fe-C超细晶/纳米晶粉末的过程中,颗粒尺寸随球磨时间和转速的增加而得到有效细化。当球料比为20:1、转速350r/min、球磨70 h时,颗粒细化效果最好。将球磨后平均颗粒尺寸为纳米级的粉末进行SPS烧结,烧结温度700℃时,能实现烧结体完全致密,并可有效避免晶粒的长大,该烧结体材料抗压强度达2800MPa。     

放电等离子烧结制备超细晶粒W-TiC复合材料

采用机械合金化和放电等离子烧结(SPS)技术制备了纳米TiC颗粒弥散增强超细晶W-TiC复合材料,对超细晶W-TiC复合材料的显微组织和室温力学性能进行了研究。研究表明,采用SPS工艺于1700℃下烧结1min可获得烧结颗粒结合良好,致密度高达约98.6%的超细晶W-TiC复合材料。通过添加纳米TiC,不仅能抑制W晶粒的长大,还能促进W的致密化。当TiC的加入量为0.7%时(质量分数,下同)可获得晶粒尺寸为0.5μm,抗弯强度和维氏硬度分别为1262MPa,6.45GPa的超细晶W-TiC复合材料。     

90W-7Ni-3Fe纳米晶粉末的瞬时液相强化烧结特征

采用机械合金化(MA)制备了晶粒尺寸为8～18 nm的90W-7Ni-3Fe纳米晶粉末(MA粉末).将粉末注射成形,在1 480～1 500℃经3～5 min瞬时液相烧结.结果表明,采用瞬时液相强化烧结可以得到W晶粒为3～8 μm近全致密的细晶钨合金,显微组织为细小的球形W晶粒均匀地连续分布在纤维状粘结相中,烧结坯具有好的拉抻性能.长时间的传统液相烧结使球状W晶粒迅速粗化,而且密度和强度下降,但延伸率反而增加.在MA粉末中添加微量Y2O3后采用瞬时液相烧结,可以使合金抗拉强度提高到1 055 MPa,延伸率提高到16.5%.     

烧结温度对Micro-FAST制备钛微型齿轮致密化的影响

将新颖的多物理场活化烧结微成形技术(Micro-FAST)引入到钛微型齿轮的制备中,研究了烧结温度对Micro-FAST制备钛微型齿轮致密化的影响。结果表明,在1200℃烧结保温4 min,体系的相对密度即可达到90.5%。Micro-FAST的烧结致密化过程大致可分为4个阶段:预热阶段、低温保温阶段、快速升温阶段和烧结保温阶段,钛粉末的致密化过程主要发生在快速升温阶段。对烧结体系的收缩动力学曲线研究发现,在电场、力场和温度场的耦合作用下,粉末体系在450℃发生了塑性变形,在1032℃生成了局部液相。研究表明,与传统烧结法相比,多物理场活化烧结法是一种新型和高效的制备钛微型零件的良好方法。     

Densification behavior of nanocrystalline W–Ni–Fe composite powders prepared by sol-spray drying and hydrogen reduction process

This paper studied the densification behavior of nanocrystalline composite powders of 93W–4.9Ni–2.1Fe (wt.%) and 93W–4.9Ni–2.1Fe–0.03Y synthesized by sol-spray drying and hydrogen reduction process. The X-ray diffraction (XRD) analysis showed that γ-(Ni, Fe) phase was formed in the final obtained powders. Powders morphology characterized by scanning electron microscope (SEM) showed that the 93W–4.9Ni–2.1Fe nanocrystalline composite powders exhibited larger agglomeration and grain size compared with the 93W–4.9Ni–2.1Fe–0.03Y nanocrystalline composite powders. Both kinds of green compacts can obtain full density if sintered at 1410 °C for 1 h. When sintering temperature was above 1410 °C, the sintering density for both compacts decreased rapidly. In addition, the sintering density, densification rate and grain coarsening rate of 93W–4.9Ni–2.1Fe compacts were higher than those of 93W–4.9Ni–2.1Fe–0.03Y. The effect of trace yttrium on the densification behavior of nanocrystalline composite powders was also discussed.     

Transient Liquid-Phase Sintering Characteristic of W-Ni-Fe Alloy via Microwave-Assisted Heating

研究了W-Ni-Fe合金在2.45 GHz微波炉中瞬时液相烧结的致密化行为和力学性能。结果表明:微波辅助热场下的93W-Ni-Fe合金显示出优异的力学性能和快速的致密化过程,其压缩试样在1500℃下烧结5 min后,拉伸强度、延伸率、相对密度和硬度(HRC)分别是1200 MPa,16.6%,98.6%和42.0;在微波辅助热场下,试样烧结可以减少80%的烧结时间;微波辅助热场下的瞬时液相烧结有利于减少烧结时间,加快致密化过程,并且有利于钨晶粒的细化,获得组织均匀和综合性能高的W-Ni-Fe合金。     

烧结温度对快速凝固TiAl合金组织及力学性能的影响(英文)

将快速凝固Ti-46Al-2Cr-4Nb-0.3Y(摩尔分数,%)合金薄带破碎成粉末,然后通过等离子烧结(SPS)制备成块体。研究烧结温度对烧结块体的组织和力学性能的影响。在1200℃烧结时得到完全致密的块体。进一步升高烧结温度对合金密度的影响不大,但是对烧结块体的显微组织及相结构有显著影响。烧结块体主要由γ和α2相组成,随着烧结温度的升高,α2相的体积分数降低,块体合金由近γ组织演变为近层片组织,且组织逐渐粗化,但是长大不明显。1260℃烧结得到的块体组织细小、均匀,没有明显微偏析,具有良好的综合力学性能,室温压缩断裂强度和压缩率分别为2984MPa和41.5%,高温(800℃)拉伸断裂强度和伸长率分别为527.5MPa和5.9%。     

等离子放电烧结制备10ScSZ细晶块体及其烧结温度探究

采用燃烧法制备10ScSZ粉体,通过等离子放电烧结(SPS)制备10ScSZ细晶致密陶瓷块体。根据SPS上下电极间距随烧结温度的变化绘制烧结曲线,在1200℃附近电极间距最小,判断陶瓷致密化温度在1200℃左右。为验证该方法的可靠性,选取1050,1100,1150,1200,1250℃作为烧结温度分别制备样品。结果表明,在1150℃烧结的10ScSZ样品具有最高的致密度,达到99.4%,且具有平均晶粒尺寸为194 nm的细晶结构,与推测结果基本相符。该实验结果证实了在SPS烧结中通过烧结曲线判断合适的烧结温度是一种高效可行的方法。     

烧结温度和保温时间对微波制备WC-8Co硬质合金显微组织的影响(英文)

采用2.45GHz高功率多模腔微波炉制备WC8Co硬质合金,对压坯的收缩率和合金的显微组织进行研究。结果表明:液相温度出现在1300°C附近;在烧结温度1450°C下保温5min能获得几乎全致密的合金试样。微波烧结法制备的合金晶粒要比真空烧结制备的合金晶粒尺寸细小且分布更均匀。另外,WC晶粒的尺寸和分布主要取决于烧结温度;保温时间对合金晶粒的影响很小,无论在1450°C下保温多长时间WC平均晶粒的尺寸始终保持在2.7μm。     

Effect of Ni addition on the densification of TiC: A comparative study of conventional and microwave sintering

This study deals with the effect of conventional sintering and microwave sintering on the densification kinetics of Titanium Carbide (TiC) in the presence of Ni (1, 1.5, 2 wt%). TiC compacts were obtained after uniaxial pressing of powders synthesised by ball milling of Titanium and Carbon and sintering was done in the presence of Nickel. The samples prepared were subjected to conventional as well as microwave sintering. The XRD and SEM analysis were used for a study of the reaction of Ti and C powders upon addition of Ni, which reduced the sintering temperature to 1200 °C. The densification of TiC powders was due to the Ti-Ni eutectic system, the liquid phase formed at this temperature assisting the sintering process. The SEM images revealed the flake like structure of TiC in which the carbon diffused into Ti upon the addition of Ni, thereby supporting enhanced mass transfer. The XRD pattern showed the presence of Titanium Oxide (TiO₂) along with TiC which resulted in non-uniform distribution of hardness. Maximum hardness was achieved in the conventional sintered compacts which gradually increased with increase in Ni addition. The presence of the oxide phase and the formation of micro cracks resulted in non-uniform hardness for microwave sintered compacts. The maximum hardness of conventional sintered compact (375 HLD) was nearly 1.5 times more than the maximum hardness of the microwave sintered compact (250 HLD). The density of the microwave sintered compact was found to be higher by 8% than with the conventionally sintered compact.     

放电等离子烧结时间对高密度W-7Ni-3Fe合金组织性能的影响

利用放电等离子烧结技术制备高密度W-7Ni-3Fe合金,研究了烧结保温时间对合金致密度、物相、显微组织以及力学性能的影响。结果表明,在1200℃烧结5~14 min后,合金均能实现充分致密化,保温时间对相对密度影响较小。合金中的W晶粒随保温时间的延长开始尺寸变化不大,烧结11 min以上才明显长大,但大多数W晶粒尺寸仍小于5μm。烧结时间超过8min,合金中新出现一种灰色的富W组织。随保温时间延长,合金的洛氏硬度下降不大,然而抗弯强度却明显上升。合金弯曲断口形貌在较短保温时间以沿晶断裂为主,粘结相的延性撕裂和W晶粒的解理断裂随烧结时间延长逐渐增多。     

The effect of sintering temperature on densification of nanoscale dispersed W–20–40%wt Cu composite powders

Nanoscale dispersed particles of W–20–40%wt Cu were synthesized using a chemical procedure including initial precipitating, calcining the precipitates and reducing the calcined powders. The powders were characterized using X-ray diffraction and map analyses. The effect of sintering temperature was investigated on densification and hardness of the powder compacts. Relative densities more than 98% were achieved for the compacts which sintered at 1200 °C. The results showed that in the case of W–20%wt Cu composite powders, the hardness of the sintered compacts increased by elevating the sintering temperature up to 1200 °C while for the compacts with 30 and 40%wt Cu, the sintered specimens at 1150 °C had the maximum hardness value. The microstructural evaluation of the sintered compacts by scanning electron microscopy showed homogenous dispersion of copper and tungsten and a nearly dense structure. A new proposal for the variation of the mean size and morphologies of W-particles with volume percent of copper melt within the composites has been suggested.     

Microstructure and properties of liquid-phase sintered tungsten heavy alloys by using ultra-fine tungsten powders

The microstructure and properties of liquid-phase sintered 93W-4.9Ni-2.1Fe tungsten heavy alloys using ultra-fine tungsten powders (medium particle size of 700 nm) and original tungsten powders (medium particle size of 3um) were investigated respectively. Commercial tungsten powders (original tungsten powders) were mechanically milled in a high-energy attritor mill for 35 h. Ultra-fine tungsten powders and commercial Ni, Fe powders were consolidated into green compacts by using CIP method and liquid-phase sintering at 1465℃ for 30 rain in the dissociated ammonia atmosphere. Liquid-phase sintered tungsten heavy alloys using ultra-fine tungsten powders exhibit full densification (above 99% in relative density) and higher strength and elongation compared with conventional liquidphase sintered alloys using original tungsten powders due to lower sintering temperature at 1465℃ and short sintering time. The mechanical properties of sintered tungsten heavy alloy are found to be mainly dependent on the particles size of raw tungsten powders and liquid-phase sintering temperature.