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.     

钨渗铜复合材料致密化机理研究

以粗细钨粉和铜丝为原料,采用粉末冶金工艺制备钨骨架,随后通过液态熔渗铜的方法制备低铜含量(质量分数低于10%)的钨渗铜复合材料。利用电子天平、金相显微镜和扫描电镜分析材料的致密度及显微组织,对材料在制备过程中的致密化机理进行探讨。结果表明:钨渗铜复合材料熔渗过程的驱动力既有毛细管力又有晶界扩散作用,熔渗路径可用根系模型来阐释;在钨骨架中加入Ni等诱导金属可强化熔渗过程;低铜含量的致密钨渗铜复合材料需制备高致密度且具有联通晶界或孔隙的钨骨架。     

低温加压烧结对钨铜复合材料致密化的影响

将W-15%(质量分数)Cu粉机械合金化后,研究无压和低温加压烧结条件下钨铜复合材料显微组织、相对密度的变化。结果表明,低温加压烧结能显著提高钨铜复合材料的相对密度,促进其烧结成形。     

纳米钨铜复合粉末的制备及其烧结行为研究

以钨酸钠和硝酸铜为原料,采用水热合成-共还原法制备钨铜复合粉末,再通过真空热压烧结法制备钨铜复合材料,并研究了钨铜复合粉末的结构形貌,以及经不同温度热处理后钨铜复合材料的显微形貌、物性特征。结果表明:采用水热合成-共还原法可制得粒度尺寸约为70nm且颗粒分布均匀的纳米级钨铜复合粉末。钨铜复合粉末经加压烧结及热处理后可得到W相和Cu相紧密结合、Cu相均匀分布在W相周围的钨铜复合材料,其在热处理温度为950℃时致密度最高,达到99.2%;在热处理温度为800℃时导电率最高,达到46.5%IACS;在热处理温度为900℃时布氏硬度最高,达到HB285。     

钨铜复合材料致密化问题和方法

在常规溶渗、烧结条件下金属钨和铜之间互不溶解,浸润特性能差,使两种粉末复合的致密化过程进行相对困难。阐述了如何提高该系统致密化过程和速度,弱化致密化条件,获得均匀弥散且两相分别连续分布的组织结构,并实现对成分和尺寸的准确控制。结合各类应用的性能要求,对钨铜复合材料致密化的各种方法进行分析和讨论,试图为选择高性能钨铜复合材料加工方法提供依据。     

钼钨合金烧结致密化行为

采用原位测量法研究了放电等离子烧结与真空热压烧结Mo–30W合金收缩和致密化行为。研究结果表明:采用放电等离子烧结Mo–30W合金时，1200 ℃以下Mo–30W合金以膨胀为主，1200 ℃以上合金开始剧烈收缩，1600 ℃以上合金收缩趋于停止，在降温阶段合金有较大收缩，温度接近室温时，收缩基本停止。经过1600 ℃放电等离子烧结后合金的相对密度可达93%以上，优于相同温度下真空热压烧结合金的相对密度89.98%。     

高钨钨-铜复合材料的研究现状

综述近几年来高钨含量的钨,铜复合材料的研究现状,对其制备方法、烧结性能及热导影响因素作了较全面的介绍。     

注射成形铜-钨复合材料烧结工艺研究

采用注射成形工艺制备了CuW5、CuW10和CuW15系列复合材料.实验从控制烧结样品微观结构的角度出发,对三种成分的CuW复合材料进行了不同温度下的烧结.重点考察了烧结温度及保温时间对烧结坯微观结构的影响,探讨两相不溶的复合材料的烧结致密化行为,同时对烧结坯的综合性能进行了检测.实验结果显示,CuW复合材料注射坯经一...     

成形压力与粉末粒径对钨铜复合材料烧结性能的影响

为进一步提高钨铜合金的致密度和简化制备工艺,研究了粉末粒度与成形压力对无压烧结制备的W-15Cu复合材料致密度的影响.发现随着球磨时间延长,钨铜粉末发生明显的细化和圆化,粉末分布更为均匀,烧结活性有较大提高,合金性能更加优异,组织结构更加良好,致密度相应提高.通过对烧结试样密度和铜含量的测定,得到不同成形压力下材料致密度和铜含量随烧结温度的变化曲线,发现随着成形压力增大,材料的烧结致密度升高,铜流失的现象得到一定的控制.     

纳米钨铜复合粉末的压制成形研究

采用黄培云压制理论研究了纳米钨铜粉的压制行为,探讨了成形压力对坯料烧结性能的影响。结果表明:纳米钨铜粉末比纳米钨粉容易压制,铜含量越多越容易压制;细粉末钨粉或钨铜粉末的压制成形能力较差,粗粉末成形能力较好;采用单向压制,W-20%Cu(质量分数)在成形压力为500～600MPa时出现明显的裂纹;在300MPa时可以获得组织均匀、致密度为99.5%的烧结样品。     

On Modeling the Kinetics of Densification of Polydispersed Powders during Sintering

A mathematical model of the densification kinetics of polydispersed powder in sintering was analyzed. The model is based on a kinetic equation which assumes that the mass-transport mechanism is grain boundary diffusion. The volume change of the powder was considered as the sum of volume changes of narrow size fractions. The case of log-normal particle size distribution was examined in detail. It was determined that the theory agrees qualitatively with known experimental results.     

Densification of Powders by Particle Deformation

Abstract

Based on a previous experimental study of particle deformation during powder compaction, a model is developed for describing the densification behaviour of an irregular packing of spherical particles. Using the radial density function of a ‘random dense packing’, the increase in both the average size and the number of contact faces are calculated. A simple criterion for local yielding allows the compaction pressure to be determined for relative densities up to 90%. In the final stage of compaction, particle deformation, now constrained by neighbouring contacts, is modelled by extrusion into the remaining pore space. A compaction equation encompassing both stages is presented; its application to non-spherical powders elucidates the role of particle shape during powder densification. PM/0150     

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.     

改善厚料层烧结热态透气性的研究

针对厚料层烧结过程中,因料层自动蓄热导致下部燃烧带过宽,热态透气性下降,影响垂直烧结速度,进而影响烧结矿产量的问题,通过实验研究分析了烧结过程中高温带宽度、温度分布特征及规律、以及燃料迁移、不同粒度燃料燃烧效率等对热态透气性的影响;提出了优化燃料粒度、改善燃料燃烧性、采用燃料分加结合熔剂分加等改善烧结过程热态透气性的技...     

热等离子制备球形纳微钨粉及烧结性能和应用研究进展

球形钨粉对于开发高附加值的产品具有十分重要的意义。热等离子技术是制备球形钨粉的有效手段。文章综述了热等离子制备球形纳微钨粉及其烧结性能,等离子球化得到的球形微米钨粉具有各向同性、堆积密度大等特点,有助于得到孔隙均匀贯通的多孔钨基体;等离子制备得到的近球形纳米钨粉分散性好、具有较高的烧结活性且特殊的形貌对晶粒的生长表现出较好的抑制作用。最后总结了球形钨粉在过滤材料、电子材料以及复合材料等领域的应用研究进展,球形钨粉因其特殊的形貌在上述领域具有极其广阔的应用前景。     

金刚石/Cu复合材料的烧结致密化研究

金刚石/Cu复合材料是性能优异的新型高导热低膨胀热管理材料.采用金刚石经表面镀Ti或Cr后再镀Cu, SPS烧结制备金刚石/Cu复合材料.结果表明: 金刚石/Cu复合材料的烧结致密化与金刚石的体积分数、粒度大小、烧结温度及形成的金刚石/金属间的界面相关.金刚石的体积分数对烧结致密化影响最大, 烧结温度影响最小; 随金刚石体积分数和粒度的增加, 金刚石/Cu复合材料的烧结致密化难度增大.     

Microstructure and Mechanical Properties of a High-Strength Ti-4Al-2Fe-3Cu Alloy Fabricated by Sintering and Hot Extrusion

A Ti-4Al-2Fe-3Cu (wt pct) alloy containing only low-cost alloying elements was fabricated by vacuum sintering a blend of TiH₂, Al, Fe, and Cu powders at 1200 °C for 1 hour followed by hot extrusion at the same temperature. The as-extruded alloy exhibited a microstructure consisting of mainly α/β lamellar colonies and Ti₂Cu as a minor phase. The average colony size and lamella thickness were 118 and 12 µm, respectively, and Fe and Cu were predominantly distributed in the β lamellae. The as-extruded alloy had a high tensile yield strength (YS) and ultimate tensile strength (UTS) of 1248 and 1270 MPa, respectively, but a limited ductility (elongation to fracture: 2.3 pct). Annealing at 750 °C for 4 hour caused the average colony size and lamella thickness of the alloy to increase to 145 and 17 µm, respectively, and the volume fraction of the β phase decreased with the annealing. These microstructural changes resulted in a slight decrease of the YS and UTS to 1221 and 1253 MPa, but a clear increase of the ductility with the elongation to fracture reaching 4 pct. This work demonstrates that a combination of relatively low-temperature vacuum sintering, hot extrusion, and annealing can be effectively utilized to fabricate a low-cost Ti-4Al-2Fe-3Cu alloy with high strength and appreciable tensile ductility.

     

TA15钛合金挤压薄壁型材拉伸性能及差异性研究

针对"直接热挤压"和"热挤压+脉冲锻打"TA15钛合金薄壁型材的室温力学性能及差异开展实验研究。通过对型材不同位置切取的试样进行拉伸试验,获得了型材抗拉强度和屈服强度分布规律,并对性能数据分布的均匀性和一致性进行深入分析。结果表明,"直接热挤压"态型材的抗拉强度和屈服强度数值分布较分散,强度离散系数大于3.5%;而"热挤压+脉冲锻打"态型材的抗拉强度和屈服强度数值分布相对集中,不同批次型材之间的力学性能一致性较好,强度离散系数均小于3%。进一步分析表明,2种状态型材之间的性能差异与型材表面状态、表面细晶层和截面尺寸有关。脉冲锻打能够改善型材表面细晶层分布的均匀性和截面尺寸精度,从而改善型材力学性能分布的均匀性和一致性。     

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.