Quantitative determination of topological and metric properties during sintering of copper

Quantitative paths of microstructural change, represented as a variation of topological and metric properties with pore volume fraction, were experimentally determined by applying quantitative microscopy to sequences of samples sintered without compaction from two size fractions of spherical copper powder, and one size fraction of dendritic copper powder. The two spherical size fractions followed paths of microstructural change during sintering that were identical except for a scale factor. The connectivity of the pore network first increased slightly, then decreased, reaching zero at a pore volume fraction (V _V ) of about 0.08. Isolated pores begin to appear atV _V = 0.20, and increased in number. The area of the pore-solid interface at first decreased slowly, then more rapidly and ultimately linearly with pore volume fraction, as has been reported in other systems. Total curvature of pore-solid interface decreased from the positive value characteristic of the loose powder stack to a negative value, passed through a minimum, and increased toward zero as full density is approached. The area of grain boundary initially increased slowly, as interparticle contacts grew; at aboutV _V = 0.15, grain growth set in, and the grain boundary area decreased, as the mean grain intercept rapidly increased with densification. The dendritic powder had a highly irregular surface shape, and consequently a loose stack structure containing more than 90 pct porosity. The path that it followed was qualitatively, but not quantitatively, similar to that observed for the spherical powders. These observations are discussed in terms of the unit geometric processes that dominate each of the three stages of loose stack sintering.     

渗铜剂成分对烧结钢渗铜性能的影响

采用纯Cu粉、Cu-2Zn粉、Cu-2Fe粉、Cu-2Zn-2Fe粉等4种不同成分的渗铜剂,以Fe-Cu-C烧结钢为基体,在1 120～1 150℃、保温30 min工艺下渗铜,研究不同成分渗铜剂的熔渗性能及其对渗铜烧结钢力学性能的影响。结果表明:同其它3种渗铜剂相比,Cu-2Zn-2Fe渗铜剂渗铜性能最好,烧结钢渗铜后表面质量均匀一致、无溶蚀现象;上下表面硬度基本一致,较未渗铜烧结钢提高了约60%;4种渗铜剂渗铜的烧结钢冲击韧性为13.7～14.0 J/cm2,较未渗铜的提高2倍以上;在渗铜剂中,Fe元素可以降低渗铜剂熔体活性、增加黏度;Zn元素可以降低渗铜剂熔体黏度、增加其活性。     

微波烧结对粉末冶金铜材显微组织与性能的影响

用微波工艺烧结铜粉压坯,用排水法、布洛维硬度计、拉力试验机测量试样的相对致密度、硬度及拉伸性能,结果表明:在30min内将微波烧结温度由室温升高到1 000℃再保温10min即可获得相对密度达92.68%的烧结试样,其硬度和延伸率均高于相同温度下的常规烧结试样,但抗拉强度略有降低.还用扫描电镜和光学显微镜观测、分析试样显微组织及断口形貌,结果显示:微波烧结试样的晶粒比常规烧结试样的细小且孔隙分布均匀.     

真空烧结温度对铜基减磨材料性能的影响

以铜粉、锡粉、铅粉等为原料,采用“压制-烧结”工艺制备了铜基减磨材料,烧结采用真空无压烧结和还原气氛保护烧结两种工艺方法.运用对比试验的方法,探讨了真空无压烧结工艺中不同烧结温度对铜基减磨材料烧结体性能的影响.结果表明:真空烧结工艺与还原气氛保护烧结工艺相比,相同的烧结温度下材料的孔隙度、抗拉强度、抗压强度和硬度变化不...     

渗铜处理对烧结硬化合金钢齿轮特性的影响

用不同硬化能参数的烧结合金钢分别压制成正齿轮坯体与扇型耐磨坯体,再同时进行1120℃×30min的烧结,而后以48℃/min的冷却速率来控制烧结钢的相变化,接着在相同条件下对其进行渗铜处理,最后对烧结体进行表面硬度、耐磨性与齿轮特性等试验.研究结果显示渗铜处理对烧结硬化合金钢的硬度、齿破裂负载以及耐磨性均有提升的效果,惟对齿轮精度则有不利的影响.FC0208烧结态的耐磨性为0.88×10-8,经渗铜处理后耐磨性则只提高到1.03×10-8;而烧结硬化合金钢的耐磨性能均较FC0208烧结钢的优异,其中以富镍的FLNC4408烧结硬化合金钢经渗铜处理后的耐磨耗性能最佳,其耐磨性可提升到3.22×10-8.然而,烧结硬化合金钢FLNC4408 0.2%Cr的耐磨耗性反而不如FLNC4408,其主要原因在于含铬成份的烧结合金钢压缩性较差,且需在较苛刻的保护气氛中进行烧结.     

烧结温度对石墨/铜复合材料微观组织与性能的影响

通过超声波分散结合机械球磨湿磨法对铜粉和石墨粉进行混料,利用放电等离子烧结（SPS）技术制备石墨/铜复合材料。运用扫描电镜（SEM）、X射线衍射仪（XRD）和电导仪等表征手段,研究了烧结温度对石墨/铜复合材料的微观组织与性能的影响。结果表明:超声波分散和机械球磨湿磨法可使石墨均匀分散于铜基体,并与铜基体形成良好的界面结合。当烧结温度从700 ℃升高到750 ℃,石墨/铜复合材料的相对密度、维氏硬度、抗压强度和电导率分别提高了1.6%,6.7%,11.3%和5.3%;当烧结温度从750 ℃升高至900 ℃时,其相对密度、维氏硬度、抗压强度和电导率均呈现下降趋势。当烧结温度为750 ℃时,石墨/铜复合材料组织均匀致密,平均晶粒尺寸约为6.4 μm,相对密度为96.3%,维氏硬度（HV_0.5）为60.7,抗压强度为422 MPa、电导率为86.7%IACS,综合性能较优。      

微波烧结碳纳米管增强铜基复合材料的显微组织与力学性能

通过微波烧结与轧制相结合,制备碳纳米管(carbon nanotube,CNTs)增强铜基复合材料(CNTs/Cu),对该材料的显微组织、致密度、硬度和抗拉强度等进行分析与测试,并通过正交试验优化工艺参数。结果表明:CNTs的最佳含量(质量分数)为2.0%,在烧结温度为1 000℃,保温时间为30 min条件下制备的2.0%CNTs/Cu复合材料,CNTs均匀分散在Cu基体中,CNTs与Cu基体结合良好,材料致密度达到98.09%,维氏硬度(HV)为372,屈服强度和抗拉强度分别达到234 MPa和344 MPa,比微波烧结纯铜分别提高18%和24%左右。     

Spark plasma sintering of cryomilled copper powder

Abstract

The densification and sintering behaviour of a cryomilled copper powder (grain size of 17±2 nm and dislocation density of 6·26±0·04×10¹⁶ m^?2) were investigated and compared to those of an atomised copper powder with the same mean particle size in order to highlight the effect of the nanostructure on spark plasma sintering (SPS). Oxygen and nitrogen contamination of the cryomilled powder gives rise to extensive degassing during SPS up to 400°C. The cryomilled powder is more resistant to plastic deformation than the atomised one, but the huge density of dislocations and grain boundary activates sintering at low temperature. Densification is therefore promoted by deformation in the atomised powder and by sintering shrinkage in the cryomilled one. As a consequence, in the SPS conditions investigated, the atomised specimen is densified but not sintered, while the cryomilled one is effectively sintered and consequently densified.     

Surface tension and the sintering force in copper

The sintering force, defined as the uniaxial tensile force necessary to just stop the sintering contraction in the direction of the applied force, has been measured over the entire course of the sintering of an uncompacted copper powder. The force rises to a maximum at a den-sity of 95 pct, and then becomes immeasurable. The sintering force perpendicular to cross-section “a” of a sinter body can also be computed from the known surface tension γ of the metal, the average mean curvature ˉH of the surface of the porosity and the area fraction of porosityA _A , by use of the relationship:F = γˉHA _A a. The calculated sintering force is valid so long as the metal-void interface is composed of a multiply-connected minimal-area sur-face. This condition is met during late first stage and early second stage sintering. Under the same conditions, the surface tension of a sinterable solid can be determined through a measurement of the sintering force.     

Structure formation during the sintering of powder steels alloyed with copper,chromium, and phosphorous

The process of structure formation during the sintering of powder steels alloyed with copper, chromium, and phosphorous was investigated. The microstructure of the materials, and distribution of alloying elements in the iron grains, were studied by the methods of electron and scanning electron microscopy. The effect of dispersion of the ferrochromium powder on its solubility in iron was examined.Kirov Factory for the Manufacture of Articles from Metal Powder. Translated from Poroshkovaya Metallurgiya, Nos. 5/6, pp. 56–62, May–June, 1995.     

铜粉激光烧结致密化过程数值模拟

通过建立金属粉末直接激光烧结过程的微观模型,对铜粉激光烧结行为进行数值模拟和实验研究,探索激光烧结致密化特征及烧结工艺、材料物性等对烧结过程和质量的影响.结果表明:激光烧结过程主要经历2个阶段:第一阶段表现为孔隙在金属熔体中的消除(约10-4s),实现快速致密化;第2阶段为熔膜的铺展或收缩引起形貌变化,但熔体中仍残留微孔,致密度基本不变.熔体表面张力、粘性、润湿性和熔膜厚度等因素对致密化进程有不同程度的影响.     

基于铁矿粉高温特性互补的烧结优化配矿

首先测定巴西、澳洲及中国的10种铁矿粉的高温特性,将其与实际生产统计所得的高温特性适宜区间比较可知:巴西矿的同化性偏低,澳洲矿偏高,中国精粉则相对接近适宜区间;有两种巴西矿、一种澳洲矿以及一种中国精粉的液相流动性适宜,一种巴西矿、一种澳洲矿以及两种中国精粉则偏低,一种澳洲矿和一种中国精粉的液相流动性稍高;澳洲矿的黏结相自身强度偏低,巴西矿和中国精粉则较为适宜,且中国精粉相对更高.在实验研究的基础上,提出基于铁矿粉高温特性互补而使混合矿高温特性指标适宜的烧结配矿新思路,并设计优化配矿方案,烧结杯实验结果显示均获得优良的烧结指标,证实了基于铁矿粉高温特性进行配矿的优越性.