粉末冶金钼合金热锻的性能和显微组织研究

【作者】 罗明；

【导师】 范景莲；

【作者基本信息】 中南大学 ， 粉体材料科学与工程， 2009， 硕士

【摘要】 Mo-Ti-Zr合金(Titanium-Zirconium-Molybdenum Alloy)具有高温强度高、抗蚀性能强以及高的抗蠕变性能、高热导率、低的热膨胀系数等优点而应用于电子、冶金、航空航天、原子反应堆等。传统粉末冶金法制备的Mo-Ti-Zr合金由于具有一定的孔隙,使其强度和韧性大大降低,限制了Mo-Ti-Zr合金的应用范围。围绕提高粉末冶金Mo-Ti-Zr合金密度和性能,论文采用采用冷等静压和高温烧结制备了Mo-Ti-Zr合金棒材,对高温烧结制备的Mo-Ti-Zr合金棒材进行高温旋锻形变强化处理,系统研究了烧结温度、旋锻温度、变形量、旋锻过程中的中间退火时间、退火温度对Mo-Ti-Zr合金棒材力学性能和显微组织的影响,探讨了孔隙和第二相粒子对旋锻Mo-Ti-Zr合金棒材的性能和显微组织的影响机理,研究结果如下：(1)随烧结温度的升高,Mo-Ti-Zr合金棒材经过高温旋锻后密度提高变小而硬度提高更加明显,抗拉强度的提高变小。在1800℃烧结的Mo-Ti-Zr合金棒材经过高温旋锻后性能最好,抗拉强度650Mpa,延伸率1.5%。随烧结温度的提高,Mo-Ti-Zr合金棒材旋锻后大尺寸晶粒更容易产生合并长大而粗化,Mo-Ti-Zr合金棒材旋锻后穿晶解理断裂的比例增加。(2)Mo-Ti-Zr合金棒材在1200℃旋锻的密度、硬度和抗拉强度比1400℃旋锻要高。采用低碳钢包套可以降低锻造温度,有效的避免Mo-Ti-Zr合金棒材晶粒的过分长大。随断面收缩率的增加,Mo-Ti-Zr合金棒材的密度和硬度、强度逐步提高。断面收缩率为27%时,Mo-Ti-Zr合金棒材密度为9.83g/cm3,硬度为HRB95,强度为648Mpa。Mo-Ti-Zr合金棒材烧结态断口主要是沿晶脆性断裂,断面收缩率为27%时,断口呈穿晶和沿晶混合型断裂。(3)随旋锻过程中的中间退火时间的增加,Mo-Ti-Zr合金棒材的密度和硬度逐渐提高,中间退火时间在40min, Mo-Ti-Zr合金棒材抗拉强度达到最大值。当退火温度低于1000℃时,随退火温度的升高,Mo-Ti-Zr合金棒材硬度末出现急剧下降,抗拉强度和延伸率逐渐提高,在900℃退火,合金棒材抗拉强度达到669Mpa,延伸率达到3.1%,获得良好的综合力学性能。(4)Mo-Ti-Zr合金棒材孔隙消除机理主要是高温使闭合之后的孔洞表面形成物理冶金结合与三向压应力使各种微裂纹焊合。Mo-Ti-Zr合金棒材第二相粒子(Mo,Zr,Ti)xOy有利于细晶强化和弥散强化,但同时因其与钼晶粒的界面结合较弱而易于产生微裂纹和促进再结晶,使晶粒发生长大降低合金的拉伸性能。更多还原

【Abstract】 Molybdenum-Titanium-Zirconium alloy is a unique refractory metal combined with remarkable high-temperature strength,corrosion resistance and creep-resistance, high thermal conductivity, low coeffcient of thermal expansion, so that it has been widely used in electronic industries,metallurgies,aerospaces and nuclear reactor vessels. The conventional PM Mo-Ti-Zr alloys have the pores and cause the decrease of tensile strength and elongation,so the application of Mo-Ti-Zr alloys are limited.In order to increase the density and mechanical properties of PM Mo-Ti-Zr alloy, Mo-Ti-Zr alloy rods were prepared by cold isostatic pressed and high temperature sintered, and the high temperature sintering alloy rods were rotary forged.The influences of sintering temperature,rotary forging temperature,deformation amount,intermediate annealing time during the rotary forging process and annealing temperature on mechanical properties and microstructure of Mo-Ti-Zr alloy rods were investigated and the influences of the pores and the second phase particles were analysed,the results are as follows:(1) The increase of density and tensile strength of Mo-Ti-Zr alloy rods rotary forged decrease, the increase of hardness is obvious with increasing sintering temperature. Mo-Ti-Zr alloy rods sintered at 1800℃reach the max value, tensile strength is 650Mpa and elongation is 1.5%.The large grains of Mo-Ti-Zr alloy rods rotary forged easily merge and coarse and the scale of transgranular fracture increase with the increasing sintering temperature.(2) The density,hardness and tensile strength of Mo-Ti-Zr alloy rods rotary forged at 1200℃are higher than at 1400℃.The low carbon steel can reduce forging temperature and effectivly avoid the grains excessive growing.The density、hardness、tensile strength increase slowly with the increasing deformation amount. The density of Mo-Ti-Zr alloy rods reach 9.83g/cm3, hardness is 92.8HRB and tensile strength is 648Mpa after rotary forging to deformation amount of 27%. The fracture type of sintering Mo-Ti-Zr alloy rods is intergranular fracture,the fracture type of Mo-Ti-Zr alloy rods is changed to the mixing type of transgranular fracture and intergranular fracture after rotary forging to deformation amount of 27%.(3) The density and hardness increase slowly with the increasing intermediate annealing time during the rotary forging process. The tensile strength reach maximum at 40min.The hardness decrease slowly and tensile strength and elongation increase with increasing annealing temperature before 1000℃. Tensile strength and elongation reach maximum 669Mpa and 3.1% at 900℃.(4) The pores disappearance mechanics of Mo-Ti-Zr alloy rods is mainly physical metallurgical bonding of the surface of the pores closing at high temperature and three-dimensional compressive stress make the microcracks welded together. Though the second phase particles (Mo,Zr,Ti)xOy produce fine grain strengthening and dispersion strengthening,they avianize interface between molybdenum grains and result in fracture and recrystallization and the molybdenum grains growth occur and the mechanical properties decrease.更多还原