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WC/Al203-Cr-Mo-Ni金属陶瓷的制备及其组织、力学性能的研究
【作者】 刘小平；
【导师】 罗兵辉；
【作者基本信息】 中南大学 ， 材料学， 2011， 硕士
【摘要】 挤压模具是白铜合金挤压设备的关键部件,白铜管热挤压模工作时承受温度高,压力大,金属陶瓷的耐磨性、红硬性及韧性不够,且易产生裂纹,塌陷变形等不足,本文针对成形模具对陶瓷材料的要求,从提高陶瓷模具材料的综合力学性能出发,采用多元微米复合成功制备出具有较高综合力学性能的WC/Al2O3-Cr-Mo-Ni金属陶瓷模具材料。论文系统研究了复合材料的高能球磨工艺、材料组分、热压烧结工艺、力学性能、微观结构及抗热震性能的关系,并对WC/Al2O3-Cr-Mo-Ni金属陶瓷模具材料的增韧补强机理进行了探讨。论文研究了高能行星球磨制备金属陶瓷单质粉末及复合粉末的工艺方法,制备出尺寸细小分布均匀的复合粉末,研究了WC、Al2O3和金属Ni的含量对WC/Al2O3-Cr-Mo-Ni陶瓷模具材料力学性能和微观结构的影响,并对其热压烧结工艺参数进行了优化,最终成功研制了具有良好综合力学性能的WC/Al2O3-Cr-Mo-Ni陶瓷模具材料。研究表明：所研制的WC/Al2O3-Cr-Mo-Ni陶瓷模具材料的抗弯强度及断裂韧性随Ni含量的增加而提高,随Al2O3含量的增加而降低,硬度的变化趋势则相反,当Ni含量为7%、Al2O3含量为10%时,在热压烧结工艺为1500℃,压力25MPa,保温30min的条件下,该金属陶瓷具有良好的综合力学性能,抗弯强度为567MPa,断裂韧性为7.46MPa·m1/2,维氏硬度为15.24GPa,基本达到现用模具材料的水平。同样的成分在采用热等静压工艺1400℃烧结出的样品性能更优异,其抗弯强度达到623MPa,断裂韧性为7.75MPa·m1/2,维氏硬度为15.98GPa。论文探讨了WC/Al2O3-Cr-Mo-Ni陶瓷模具材料的断裂方式,研究发现随着粘接相Ni含量的增加,陶瓷材料的断裂方式由沿晶断裂向沿晶断裂与穿晶断裂相混合的方式转变,金属Ni的添加对陶瓷材料具有很好的增韧作用。研究和分析了WC/Al2O3-Cr-Mo-Ni陶瓷模具材料的增韧补强机理,其主要强韧化机制有晶内型结构强韧化、细晶强韧化、裂纹偏转、裂纹桥联、裂纹分叉,WC/Al2O3-Cr-Mo-Ni陶瓷模具材料的力学性能的提高是以上几种韧化机制复合作用的结果。WC/Al2O3-Cr-Mo-Ni陶瓷模具材料的热震临界温差△Tc为260～280K,比单相氧化铝的要高约80K,多元复合是陶瓷材料抗热震性能改善的主要原因。
【Abstract】 White copper alloy extrusion die is a key component of extrusion equipment,it suffered high temperatures and under pressure when working,and the wear resistance of metal ceramic, red hardness and toughness is not enough, and easy to crack,collapse deformation. From the requirement for die materials,multi-phase composite ceramic die materials with high mechanical properties were fabricated successfully with multi-phase composite method. The correlations among the material composition,the hot pressing process, the microstructures, mechanical properties and thermal shock resistance were investigated. The strengthening and toughening mechanisms of the multi-phase composite ceramic die materials were studied systematically.The elemental powders and the composite powders were fabricated by planet ball-milling,we have achieved the fine and uniformly powders,it is benefit to subsequently hot-pressed sintering. The effects of WC、Al2O3 and metal Ni on the microstructure and mechanical properties of multi-phase composite ceramic die materials were discussed. The hot press sintering parameters were optimized. WC/Al2O3-Cr-Mo-Ni composite ceramic composite ceramic die material was fabricated successfully. Result shows that excellent mechnical property and microstructure could be obtained only with the condition of the suitable volume fraction and the suitable HP sintering technique. With increasing Ni additions,the flexural strength and fracture toughness of the composites increased,while the hardness is decreased,with increasing Al2O3 content,the change of the mechnical property of the composite is opposited to that the addition of Ni content.WC/Al2O3-Cr-Mo-Ni composite ceramic have been developed successfully by hot-pressed at 1500℃under 25 MPa in flowing argon. A flexural strength of 567MPa, a fracture toughness of 7.46 MPa·m1/2 and a Vicker’s hardness of 15.24GPa are obtained with the addition of 7wt.% Ni and 10wt.% Al2O3 microparticles. The mechnical perporty of the same component prepared by HIP sintering is superior to than of hot-pressed sample, its flexural strength, fracture toughness and Vicker’s hardness are 623MPa,7.75MPa·m1/2 and 15.98GPa,respectively. The fracture surface of the composite was characterized by a mix of intergranular and transgranular fracture as a result of the presence of both intergranular and intragranular secondary phase particles due to the increasing of Ni content. Toughening mechanisms of multiple reinforced WC/Al2O3-Cr-Mo-Ni cermets were studied. The main toughening mechanisms are fine grain strengthening and toughening,intergranular toughneing,crack deflection,crack bridging,crack branching toughening. It is suggested that theincrement in the mechanical properties of muiti-phase reinforced WC/Al2O3-Cr-Mo-Ni ceramics is due to the combined effects of toughening mechanisms. Finally,the thermal shock resistance of composite was also studied, The critical temperature difference(△Tc) was 260～280K,higher 80K than that of monolith. Fined grains and multiphase improve the thermal shock resistance of the composites.