激光熔覆沉积Ti-20V-15Cr合金的组织演化与硬度

Microstructure Evolution and Hardness of Laser Cladding Deposited Ti-20V-15Cr Alloy

以混合的Ti、V、Cr元素粉末为原料,采用CO_2激光器激光熔覆沉积Ti-20V-15Cr阻燃钛合金,并针对合金沉积层的显微组织、冶金质量以及显微硬度展开研究。结果表明,采用CO_2激光器制备的Ti-20V-15Cr阻燃钛合金,沉积试样成分分布均匀、组织致密、未出现裂纹、熔合不良等缺陷;沉积试样整体由单相!晶粒组成,但原始!晶粒形态对激光熔覆沉积工艺下的熔池凝固条件变化极为敏感;沉积试样底部、中部和顶部区域沿沉积层生长方向依次出现三种形态的晶粒生长:柱状晶、类等轴晶和等轴晶。基于合金凝固柱状晶/等轴晶转变模型以及激光熔覆沉积过程试样底部、中部和顶部熔池凝固条件分析,揭示了激光熔覆沉积Ti-20V-15Cr合金的凝固组织形成机理,采用显微硬度计对沉积试样各区域显微硬度进行测试。测试结果表明,沉积试样各区域硬度分布均匀,未出现明显波动,平均显微硬度约为372HV。

Mixed Ti, V, Cr elemental powders were used as raw materials in the CO2 laser cladding deposition of Ti-20V-15Cr alloy. This work involved the analysis of the microstructure and the determination of the micro-hardness and metallurgical quality of alloy layer. The results showed that the Ti-20V-15Cr burning-resistance titanium alloy prepared by the CO2 laser are with uniformly distributed elements and absent of cracks, and lack of fusion defects. The whole sample deposited are composed of singlebeta-phase grains,, however, the original beta grain morphology is extremely sensitive to changes in the solidification in the molten pool during laser cladding deposition process. In terms of the processing parameters, the microstructure of the deposited samples at the bottom, middle, and top areas along the growth direction of the deposits are composed of three types of grain growth： columnar, near-equiaxed, and equiaxed. Furthermore, the formation mechanism of the laser cladding deposited Ti-20V-15Cr was elucidated by the columnar-to-equiaxed transition （CET） model under different solidification conditions of molten pool. The micro-hardness test results showed that the micro-hardness distributions of the samples are uniform within all regions with no obvious fluctuations, and the average micro-hardness is-372 HV.