【摘要】 对SiC粒子进行了多种预处理工艺试验 ,得出SiC粒子在 92 0℃高温焙烧氧化 ,再在HF酸 (1.5(vol.) % )与丙酮混合液、丙酮中清洗球磨工艺是较优的预处理工艺 .应用搅熔铸造工艺 ,处理后的SiC颗粒能较易分散到含镁的ZA - 2 7合金液中 .用SEM、EDS、XRD和TEM测定和分析了预处理前后SiC表面状态 ,得出SiC颗粒表面物理、化学吸附的气体是阻止其分散进入ZA - 2 7合金液的主要原因 ,SiC表面的微细粉末和Si4 + 离子是气体吸附源 ;确定了SiC表面SiO2 层的存在形式 ,并确定所使用SiC有三种结构类型 ,颗粒中含有游离碳 .更多还原

【Abstract】 Particulate reinforced metal matrix composites (MMCp) have attracted considerable attention in the aerospace, aircraft and automotive industries due to their distinctive properties of high specific stiffness and strength, unique wear and erosion resistance, resisting high temperature creep, good ability of conventional fabrication processes. It is found that SiC particles received as abrasive grade cannot be incorporated and dispersed in ZA-27 alloy melt or semisolid slurry by the application of stirring casting processes. To overcome the difficulty and improve the wettability of SiCp and ZA-27 alloy melt, SiC particles must be pretreated and new pretreatment technology should be explored. Various pretreatment techniques are experimentally studied, including that SiC particles are soaked and cleaned in aqueous solution containing surface active agent at different temperatures, or immersed and stirred in the HF, NaOH and Na 2CO 3 at various concentrations, respectively, oxidized in air at 900?℃～950?℃, cleaned in organic solution by an ultrosonic machine and milled in the mixed solution of HF and acetone by a planetary milling machine. Experimental results show that the oxidation, cleaning and milling in acid solution and in organic solution are dominant processes, and the concentration of HF must be limited. Comparison with experimental results, it is the best pretreatment process in which SiC particles are oxidized at 920?℃ for one hour, then milled in mixed solution of HF and acetone and cleaned in acetone for an hour, respectively. Pretreated SiC particles will not be agglomerated each other before addition to the melt, and can be easily incorporated and dispersed in semi solid ZA-27 alloy slurry by Stirring Melt Casting Process. The surface states of SiC particles before or after being pretreated are measured and analyzed by SEM, EDS, XRD and TEM. It is pointed out that gas existing on the surface of SiC by physical and chemical absorption is the main cause that prevents SiC particles from dispersing and staying in the slurry in the process of addition SiC particles. The finer SiC powders, coarse fracture surface(cleavage stages) and Si 4+ ion existing on the SiC surface are gas absorption resouces. EDS results (electron beam acceleration voltage 6 kV is used) show that changes take place in C, Si and O concentrations of SiC particulate surface by the different pretreatment processes, and specially their concentrations by the optimal pretreatment process are C 76.22 (wt.)%, O 5.15 (wt.)% and Si18.63(wt.)%. A layer of dense amorphous SiO 2 formed by the oxidation is surrounded on SiC particles, and amorphous diffraction pattern of SiO 2 is obtained by selected area electron diffraction patterns. The crystal structure of SiC used is determined to be 6H, 33R and 5R types, in which 6H structure is dominant and SiC particles include little dissociated carbon by XRD. There does not exist amorphous SiO 2 diffraction characterization in XRD spectrum. It shows that SiO 2 content is very small.更多还原