【作者】 李达人；

【导师】 王尔德；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2009， 博士

【摘要】 W与Cu属于不互溶材料,也称为W-Cu复合材料。传统上一般采取熔渗烧结或液相活化烧结工艺方法制备,但很难获得高致密度和优良的性能(主要为电导率和硬度值)。为了获得具有优良性能的高档W-Cu材料,一般还要采用真空热压或热等静压。由于真空热压与热等静压工艺生产效率低,成本高,难以获得广泛应用。为了寻找一种能够替代热等静压方法的新工艺,本文研究了Cu含量20~50wt.%范围内W-Cu材料粉末热挤压致密化,重点研究了粉末包套液相挤压制备W-Cu材料的工艺。由于W相再结晶温度(>1600℃)远高于Cu相熔化温度(1083℃)且两相不互溶,本文提出了两种粉末热挤压塑性变形致密工艺:一种是W-Cu(20~50wt.%)粉末经传统液相烧结制坯后再经热静液挤压致密,另一种是W-Cu(20~50wt.%)粉末压坯不经烧结,在1000~1150℃范围内直接包套热挤压致密,并重点研究了1100℃下的液相挤压工艺。同时,W-Cu属于难变形材料,为了进一步提高材料的性能,也为了使W-Cu产品品种趋于多样化,还对液相挤压工艺制备的W-Cu材料的塑性变形进行了研究。复合粉末的均匀程度将严重影响到块体材料的组织性能,本文首先研究了不同的混粉和球磨工艺对W-Cu粉末的影响。相比于机械混粉,低速球磨混粉能够获得细小的钨颗粒均匀分布在铜基体上的复合粉末,为保证W-Cu致密体材料的组织均匀性提供了良好的基础。对W-Cu材料液相烧结热静液挤压工艺进行了实验研究。热静液挤压工艺使液相烧结坯料的相对密度、组织和性能得到了进一步的改善。如:W-40wt%Cu挤压态坯料相对密度达到98%以上,电导率达到48%IACS,硬度值约为140HV。本文重点研究了W-Cu粉末包套热挤压致密工艺,通过实验得到了挤压温度、粉末球磨时间、挤压比、包套壁厚、铜含量和热处理工艺等因素对挤压坯相对密度及组织性能影响的基本规律。通过对相对密度、铜含量、边缘铜分布几方面的研究结果表明,1100℃挤压可以实现Cu出现液相的液相挤压工艺,并获得良好的组织性能。1100℃下挤压,坯料内部出现液相铜,大大提高了挤压坯的致密化速度和性能;但再提高挤压温度,如1150℃下挤压,坯料内部液相铜出现外渗,以及Cu相聚集形成大块的网状分布,虽然此时相对密度大幅提高,但坯料导电性能反而大幅降低。如:W-40wt%Cu粉末包套坯料在1100℃液相挤压,铜相分布均匀,钨相尺寸细小(2-3μm),相对密度达到97%以上,电导率达到56%IACS,硬度值高达215HV。对于液相挤压工艺,随球磨时间增加,挤压坯相对密度降低,导电性能也有所下降,挤压比和铜含量的增加都有助于提高挤压坯的相对密度和导电性能,当铜含量在30~50wt.%时,获得了良好的挤压效果。液相挤压在体现其工艺优势的同时,性能指标也已接近同类材料热等静压工艺的水平。通过数值模拟研究了粉末包套挤压过程中粉末多孔体和塑性包套的温度、应力应变和速度场的分布规律。讨论了挤压温度、挤压速度、挤压比、包套厚度对坯料内部最高温度及其对应的应力、最大应变以及粉末多孔体和包套流动速度的影响。通过数值模拟获得的坯料形状和挤压载荷值与实验得到的结果有很好的一致性。分复压和稳态流动两个阶段建立了粉末包套挤压的理论模型。推导得到了复压阶段的致密化方程和静水压力表达式,以及稳态流动阶段所需挤压力和挤压比、包套尺寸、多孔体相对密度的关系。最后,研究了W-Cu液相挤压致密材料再经不同塑性变形后对坯料相对密度、力学性能和组织性能的影响。结果表明,多道次轧制相对密度提高比镦粗明显,二次挤压相对密度提高最大。镦粗和轧制变形对材料性能提高不明显,多道次轧制电导率值略大于镦粗变形,硬度值相差不大。二次挤压坯料的电导率和硬度提高很显著,W-40wt.%Cu坯料的电导率高达60%IACS,硬度值超过230HV。与传统烧结工艺相比,再经热静液挤压能提高W-Cu材料的相对密度和性能;而液相挤压工艺则更进一步,省去了坯料长时间高温真空液相烧结致密过程,包套液相挤压一次致密,无需保护气氛加热,有着工艺简单、生产效率高、成本低廉、节能节时等优点,而且很好的解决了烧结过程中坯料铜相损失严重以及坯料成分难以精确控制等问题,在制备含铜30wt.%以上的W-Cu材料方面体现了极大的优势。本文两种工艺制备的W-Cu材料性能都比较好。特别是液相挤压工艺,其相对密度虽然要略低于热静液挤压,但电导率和硬度要提高很多,有望替代热等静压工艺来制备高档W-Cu材料。目前国内外还未查阅到关于热静液挤压和粉末包套热挤压工艺制备W-Cu材料的研究和专利的报导,特别是成功实现了液相铜出现的液相挤压过程。同时,对W-Cu材料塑性变形的研究也很少见。本文创造性的提出了制备不互溶合金的液相挤压新工艺并取得了良好的结果,对促进我国钨、钼合金的开发应用具有重大意义。更多还原

【Abstract】 W and Cu are liquid phase immiscible materials, also called as W-Cu composite. Generally, it is usually prepared by infiltration or liquid active sintering, but the density and properties (specific conductance and hardness) are usually unsatisfied. In order to obtain W-Cu materials in high-grade, the process such as vacuum hot-pressing or HIP is usually used to increase the relative density. Because of the low productive efficiency and high cost of vacuum hot-pressing and HIP, the application of W-Cu materials is limitted. This paper studied on the densification of W-Cu powders by hot extrusion with the Cu contents between 20~50wt.%, especially foucsed on the liquid phase extrusion process in order to substitute a new process for HIP.The recrystallization temperature of W (>1600℃) is much higher than the melting point of Cu (1083℃). Based on this feature, two different processes of powder densification by hot extrusion and plastic deformation are introduced in this paper. One is prepared by liquid sintering and hot hydrostatic extrusion, the other is prepared by canning hot extrusion between 1000~1150℃and particularly in the temperature of 1100℃. W-Cu materials is hard to be processed. So the plastic deformation of W-Cu materials prepared by liquid phase extrusion is also studied in order to diversify the product species of W-Cu as well as improving the properties.The uniformity of composite powders effects the properties of block materials severely. In this paper, the mixing and mechanical milling processes are studied. Comparing to machine mixing, the mechanical milling process with low speed can obtain composite powders of copper matrix attached by fine W particles. This structure guarantees the good uniformity of compact W-Cu materials. The liquid sintering and hot hydrostatic extrusion process is studied. After hot hydrostatic extrusion, the relative density and properties of W-Cu sintered billets are apparently improved. The relative density of W-40wt.%Cu is up to 98%, and the specific conductivity reaches 48%IACS with the hardness of about 140HV.This paper has payed major attention on the densification of W-Cu powders by canning hot extrusion. The basic regularitys on relative density and properties affected by extrusion temperature, milling time, extrusion ratio, can thickness, contents of Cu and heat treatment are experimentally studied. The relationship of extrusion temperature and the physical state of Cu is explored by the change of relative density, contents of Cu and distribution of Cu element on the edge of W-Cu materials. The result shows that, the liquid phase extrusion which means the compact with liquid Cu inside during extrusion can be achieved when the extrusion temperature at 1100℃. The appearance of liquid Cu is very helpful to improve the densification course and properties of W-Cu. When the extrusion temperature increase to 1150℃, the liquid Cu inside the compact exosmosed and aggregated to building a Cu rich zone. Though the relative density increased a lot, the specific conductivity decreased violently. After 1100℃liquid phase extrusion, the distribution of Cu inside W-40wt.%Cu material is uniform, the particle size of W is fine (2-3μm), the relative density is about 97%, the specific conductivity reaches 56%IACS, and the hardness is up to 215HV. In the liquid phase extrusion process, the relative density and specific conductivity decreased with increasing milling time, and increased with increasing extrusion ratio and contents of Cu. When the contents of Cu is between 30~50wt.%, the W-Cu materials with good properties are obtained by liquid phase extrusion. The liquid phase extrusion process has showed its advantages and obtained W-Cu materials with properties level almost reached the level of HIP process.Researched on the distribution of temperature, stress/strain and velocity fields of porous and steel can materials in powder canning extrusion process by numerical simulation. The influence on the highest temperature in the extrusion process and corresponding stress, maximum strain and the velocity of porous and steel can effected by extrusion temperature, extrusion velocity, extrusion ratio and can thickness was studied. The simulation and experimental results had reached a good agreement. Established the theoretical model of powder canning extrusion which was divided in two steps of multiple compress and steady-state flow. The densification equation and hydrostatic-pressure expression in the multiple compress step and the relationship between extrusion force and extrusion ratio, can size, relative density of porous in steady-state flow step were obtained.At last, the influence on relative density, mechanical property and structure property effected by different plastic deformation of dense materials prepared by liquid phase extrusion was studied. The increment of relative density of rolling is higher than upset, but is lower than second extrusion. The improvement of properties of W-Cu materials by upset and rolling is little, but remarkable by second extrusion. After second extrusion, the specific conductivity of W-40wt.%Cu materials reaches 60%IACS and the hardness is up to 230HV.Compared to the traditional sintering process, hot hydrostatic extrusion process can improve the relative density and properties of W-Cu. And the liquid phase extrusion process disposes the long time, high temperature vacuum sintering course and uses one-time forming technique without special atmosphere protection. It has the advantages of simple process, high productive efficiency, low cost and energy-saving/time-saving, and solves the problem of losing Cu when liquid sintering and precision controlling the percentage composition. It shows the huge priority on preparing W-Cu materials with Cu contents above 30wt.%. Either of the two process mentioned in this paper has obtained W-Cu materials with good properties. The relative density of liquid phase extrusion billet is a little lower than sintering-extrusion billet, but the specific conductivity and hardness are improved a lot. The liquid phase extrusion process is a predictable way to substitute for HIP process in preparing high-grade W-Cu materials.Recently, the research and patent reports about hot hydrostatic extrusion and powder canning extrusion of W-Cu materials have not been consulted yet, especially about the achievement of liquid phase extrusion process. At the same time, the study about plastic deformation of W-Cu is also rare. This paper creatively states a new liquid phase extrusion process to prepare immiscible alloy and obtains a good result. It shows the great importance on improving the development and application of W, Mo alloy in our country.更多还原