Cu-Ni-Fe-Co合金的烧结致密化

铝电解用连接导杆是连接阳极和电源的关键部件,在高温电解条件下起承载阳极的作用和承担大电流导通的任务,其原材料必须是导电的、有一定强度和高致密度的.该文采用粉末冶金方法制备Cu-Ni-Fe-Co合金材料,研究烧结温度对其密度及力学性能的影响,进而确定制备高致密度导杆合金材料的最佳烧结工艺.结果表明:该合金的相对密度随烧结温度的提高而提高,当烧结温度为1250℃时能获得综合性能较好、相对密度为95.2%、晶粒尺寸为20～30 μm的Cu-Ni-Fe-Co合金材料,其性能完全满足制作铝电解连接导杆的要求.     

WC/Cu复合材料组织及烧结过程研究

研究了粉末冶金冷压—烧结法制备的WC/Cu复合材料在不同温度和时间烧结时的组织变化及WC含量对烧结过程的影响,分析了该材料的烧结过程。结果表明,WC颗粒推迟了烧结进程。烧结过程中烧结体无明显收缩,WC颗粒显著阻碍了晶粒长大。WC/Cu复合材料的烧结过程可分为粘结、烧结颈长大、闭孔球化、烧结颈二次长大四个阶段     

熔渗法制备高导热金刚石/Cu复合材料

利用真空热压熔渗技术制备金刚石/Cu复合材料。研究熔渗工艺、金刚石表面镀覆条件等对制备出的金刚石/Cu复合材料的热物理性能的影响。通过理论分析和试验数据可以发现:利用熔渗工艺制备出的金刚石/Cu复合材料中增强体金刚石的石墨化程度非常低,对复合材料的热性能影响很小;提高复合材料的致密度以及降低复合材料的界面热阻是提高复合材料热导率的主要方法,通过改变工艺参数和在金刚石表面镀覆金属层等方法可以提高复合材料的致密度并降低材料的界面热阻;采用180~210μm粒径镀Cr金刚石制备的金刚石体积分数为60%、相对密度为99.1%的复合材料热导率达到462 W·m-1·K-1。     

放电等离子烧结制备非连续石墨纤维/Cu复合材料

以磨碎中间相沥青基石墨纤维和铜粉为原料,通过放电等离子烧结(spark plasma sintering,SPS)制备非连续石墨纤维/Cu复合材料,对石墨纤维表面进行镀钛金属化处理,以改善材料的界面结合状况.研究SPS工艺参数、铜粉粒度搭配、石墨纤维表面镀钛以及石墨纤维含量对石墨纤维/Cu复合材料致密度及热导率的影响.结果表明,将平均粒度为12和80 μm的铜粉按1∶2的质量比搭配,再与表面镀钛石墨纤维按1∶1的体积比混合,采用35 MPa先加压后送热的加压方式,于895℃下进行放电等离子烧结,可获得致密度达99.6％、热导率为364 W/(m·K)的石墨纤维/Cu复合材料,是1种很有潜力的电子封装材料.石墨纤维表面镀覆的极薄Ti镀层,可使复合材料在二维平面方向上的热导率从196 W/(m·K)提高到364 W/(m·K).     

放电等离子烧结法制备金刚石/Cu复合材料

通过真空镀铬对金刚石颗粒进行表面改性,采用放电等离子烧结法(SPS)制备改性金刚石/Cu复合材料;研究金刚石的体积分数、工艺参数以及金刚石颗粒表面改性对复合材料导热性能的影响。结果表明,烧结温度、混料时间以及金刚石颗粒的体积分数都会影响材料的致密度,金刚石颗粒的体积分数还会影响材料的界面热阻,而致密度和界面热阻是影响该复合材料导热性能的2个重要因素;对金刚石颗粒进行真空镀铬表面改性,可改善颗粒与铜基体的润湿性,降低界面热阻。在一定的工艺条件下,镀铬金刚石体积分数为60%时,改性金刚石/Cu复合材料具有很高的致密度,其热导率达到503.9W/(m.K),与未改性的金刚石/Cu复合材料相比,热导率提高近2倍,适合做为高导热电子封装材料。     

SiCp/Cu复合材料的SPS烧结及组织性能

以化学镀Cu包覆SiC粉末和高压氢还原法制备的Ni包SiC复合粉末为原料,用放电等离子体烧结法制备了SiCp/Cu复合材料.分析了增强相含量和烧结温度对致密化的影响,比较了非包覆粉末和包覆粉末制备的复合材料的界面结合状况.然后对SiCp/Cu复合材料的热膨胀行为和力学性能进行了研究.结果表明:包覆粉末能够促进材料的致密化并且能获得良好的界面结合,所得SiCp/Cu复合材料的致密度达96.7%,抗压强度达1061 MPa.SiCp/Cu复合材料的热膨胀系数介于7.5×10-6～11.4×10-6·K-1之间,并且随SiC体积分数的增加而降低.材料在热循环过程中出现热滞现象,热滞现象受增强相的含量及界面结合状况的影响.     

烧结温度对TiC/Cu复合材料组织和性能的影响

本文研究了烧结温度对TiC/Cu复合材料组织和性能的影响,研究结果表明,随着烧结温度的升高,骨架密度增加;渗Cu试样随着骨架密度的增加,硬度增加,而抗弯强度降低,低骨架密度TiC/Cu复合材料的抗弯显微断口有明显的韧窝,呈伪韧性断口形貌.     

高增强体含量SiCp/Cu复合材料制备和性能的研究

针对高增强体含量SiCp/Cu复合材料的高致密化问题,提出了理论模型,即采用尺寸比为10∶1的两种SiC颗粒,在适当的配比下可制得高致密度的SiCp/Cu复合材料.采用非均相沉淀包覆法(Heterogeneous precipitation process)(简称包覆法)制得Cu包SiC复合粉体,利用热压工艺制备了含有50%(体积分数)SiC颗粒的SiCp/Cu复合材料.用扫描电镜(SEM)对试样进行断口形貌分析,结果表明,细颗粒SiC可以有效地促进试样的致密化.对试样孔隙度的检测结果表明,随着细颗粒SiC含量的增加,试样孔隙度下降.试验结果很好地验证了理论模型.对试样的硬度、抗弯强度和电阻率的研究结果表明,随着细颗粒SiC含量的增加,试样的抗弯强度和硬度提高,而电阻率的变化不大.     

铝电解用铜基连杆材料的烧结致密化及其抗氧化性

为了获得致密的铝电解用铜基连杆材料,采用粉末冶金方法制备了Cu-Ni-Fe-Co合金材料,研究了该合金的烧结致密化过程及最佳致密度下该合金的抗氧化性能.结果表明:该合金的致密度随烧结温度的提高而提高,较低的烧结温度1 050℃难以实现致密化,但过高的烧结温度1 280℃容易使样品发生变形,烧结温度为1 250℃时能实现致密化且样品不发生变形;该合金的致密度随压制压力的增大有所提高,但超过600 MPa后,增幅趋于平缓.在较优的条件下可以制备出致密度为95.2%,晶粒尺寸为20～30 μm的合金,该合金力学性能良好,且在850℃空气中氧化动力学遵循抛物线规律,这证明合金表面形成了致密的复合氧化膜,随着反应时间的增加氧化膜具有保护作用.     

褐铁矿致密化烧结技术试验研究

分析了褐铁矿的烧结特性及成矿机理,根据性能优势互补配矿理论,通过试验将褐铁矿与镜铁矿合理搭配进行烧结.试验结果表明：褐铁矿烧结性能得到强化,烧结矿指标明显改善,主要是镜铁矿液相生成温度高、流动性差,褐铁矿颗粒被镜铁矿包裹,使得褐铁矿颗粒在与液相接触之前得到致密,避免了脆化结构的形成.褐铁矿致密化烧结使得烧结矿的矿物结构发生变化,多孔薄壁结构减少,有利于改善烧结矿高温性能.     

A Phenomenological Analysis of Sintering Mechanisms of W-Cu from the Effect of Copper Content on Densification Kinetics

The effect of addition of copper on the sintering of a W powder was systematically investigated by the analysis of dilatometric experiments on W and W-Cu compacts prepared with submicrometric powders. A pure W powder compact and a W-10 wt pct Cu powder compact with the same packing fraction of W particles were first studied, in order to analyze the effect of copper at fixed microstructure of the solid W particle packing. A more systematic set of experiments with different copper contents and W particle sizes was also qualitatively analyzed. A phenomenological model of sintering was developed and fitted in order to extrapolate the effect of copper content on sintering kinetics at fixed microstructure of the W particle skeleton. An interpretation of the sintering mechanisms was then proposed. Sintering of a W-Cu powder compact is the result of solid-state sintering of the W skeleton, enhanced by the capillary forces exerted by copper, with the superimposition of a particle rearrangement step after copper melting.     

Nd-Fe-B磁体烧结致密化过程的研究

定量描述了Nd-Fe-B磁体的烧结致密化过程, 分析了有效稀土含量、合金粉末粒度与烧结致密化过程的关系, 讨论了Nd-Fe-B磁体烧结过程的致密化机制. Nd-Fe-B磁体烧结致密化过程可分为3个阶段, 即致密化过程迅速进行阶段、缓慢进行阶段、相对稳定阶段;随着烧结温度的上升, 第一阶段表现得更为突出, 第二阶段对应的烧结时间区段大大缩短. 有效稀土含量的提高、合金粉末粒度的减小显著促进Nd-Fe-B磁体烧结致密化过程. 主相颗粒重排以及主相颗粒长大与形状适位性变化是Nd-Fe-B磁体烧结过程的两类主要致密化机制, 而且后者对于Nd-Fe-B烧结磁体实现完全致密化起着决定性的作用.     

金刚石对青铜基砂轮胎体烧结机制影响的探讨

通过XRD衍射及能谱分析发现:由于Sn对金刚石的润湿作用,会使青铜基砂轮胎体的熔化-溶解-析出机制加速完成,从而促进高温合金相Cu_(40.5)Sn_(11)迅速发生分解。而未加入金刚石时,熔化-溶解-析出和扩散-固溶两个烧结机制进行得都比较缓慢,导致高温合金相Cu_(40.5)Sn_(11)分解不充分,室温时还保留此相。     

Refinement of Master Densification Curves for Sintering of Titanium

An approximate master curve for the densification of cold-pressed titanium powder during vacuum sintering was published previously. It was based on the combined results for three different titanium powders. The master densification curve model incorporates the effects of particle size, compaction pressure, sintering time, and sintering temperature on densification. The collection of a large amount of additional data now allows refinement of the model. Distinct curves are presented for three different titanium powders, prealloyed Ti6Al4V, and Ti-Ni binary alloys. The master densification curve is sigmoidal, but deviates from the ideal form at high sintered density; the relative sintered density saturates at 90 to 100 pct, depending on the particle size of the titanium powder, and to a lesser extent the compaction pressure. The master densification curve below the saturation level is slightly dependent on the compaction pressure.     

钨铜粉末材料烧结-挤压致密化研究

为探索难熔金属和铜粉末混合坯致密化工艺,提出了钨铜粉末材料液相烧结和热静液挤压致密新工艺,经过实验获得了近致密、组织细小、性能优异的复合材料.结果表明,WCu40混合粉末冷压坯的相对密度约为70%,经过液相烧结和热静液挤压,可以获得相对密度大于99.8%的钨铜(WCu38)材料.致密后材料导电率可达到41～48 m·Ω-1·mm-2,硬度可达到HB173～176.     

Fast Sintering of Nanocrystalline Copper

The behavior of nanocrystalline (nc) copper specimens obtained by high energy ball milling (HEBM) and electromagnetic field-assisted sintering under stress and mechanical compression is explored. High yield stress values combined with plastic behavior are observed. The basic densification mechanisms involved in the production process and the peculiar action on the dislocation network are discussed.     

球磨时间对W-30Cu复合粉末中W晶粒度及烧结致密化行为的影响

研究了高能球磨时间对W-30Cu复合粉末晶粒度及烧结行为的影响.结果表明,当球磨时间从16h提高到33h时,复合粉的晶粒度由25nm减小到10nm,并发生机械合金化现象;在温度为1275℃烧结60min,经18h高能球磨的复合粉末烧结就可以达到全致密.研究还发现,高能球磨W-30Cu复合粉末具有较好的热稳定性,经950℃退火处理,晶粒尺寸没有发生异常长大现象;经烧结材料的硬度明显高于普通的W-30Cu复合材料.经1 275℃烧结30 min后合金其晶粒尺寸在300～550 nm.     

The Structural Evolution and Densification Mechanisms of Nanophase Separation Sintering

Nanophase separation sintering (NPSS) facilitates low temperature, pressureless sintering through the formation of solid phase necks driven by phase separation. Systems that have been shown to exhibit this phenomenon are W–Cr, Cr–Ni and to a lesser degree Ti–Mg. Initial information on the average rate-limiting sintering kinetics in these systems was obtained using traditional master sintering curve analysis, but it is very clear that multiple processes occur during NPSS, and these should each have their own characteristic kinetics. Here we analyze these three systems in greater kinetic detail using densification rates in a Kissinger-style analysis derived explicitly for densification data. For the W–Cr and Cr–Ni systems two critical temperatures were identified: one at low temperatures for the formation of the secondary phase necks, and a second one at high temperatures corresponding to the onset of rapid densification. The activation energies of these processes are different, and reflective of bulk solute diffusion and interdiffusion, respectively. Combined with microstructural observations, these data show that the onset of rapid densification at high temperatures is facilitated by the presence of the second-phase necks, and occurs at the point where the system can fully interdiffuse, rehomogenizing those necks. These observations help explain why the Ti–Mg system does not densify well, because it does not exhibit redissolution at high temperatures. These results help clarify the conditions needed to achieve NPSS and may support design of new alloys for NPSS behavior.

     

Sintering Densification and Microstructure Formation Kinetics in Silicon Nitride Ceramics

Research has been done on how the shrinkage rate and microstructure in the Si₃N₄ Al₂O₃ Y₂O₃ are dependent on temperature and nitrogen pressure during sintering. The shrinkage rate curves alter as the activator content varies. Additional densification may occur above 1800°C because of diffusion through the increased amount of liquid.