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    残余应力对选区激光熔化成形工业纯铁应力腐蚀行为的影响

    Effect of Residual Stress on Stress Corrosion Behavior of Industrial Pure Iron Formed by Selective Laser Melting

    • 摘要: 采用选区激光熔化成形工业纯铁试样,进行不同温度(650,800,950 ℃)固溶+400 ℃时效处理以调控残余应力,在不同质量分数(3.5%,5.0%,10.0%)NaCl溶液中进行慢应变速率拉伸试验,研究了残余应力对成形试样应力腐蚀行为的影响。结果表明:沉积态成形试样中较高残余拉应力的存在提升了其在较高Cl浓度(质量分数不小于5.0%)下的应力腐蚀敏感性,随着Cl浓度增加,应力腐蚀敏感性增大;固溶+时效处理后,残余应力降低,其在较高Cl浓度下的应力腐蚀敏感性降低,且随Cl浓度增加,650,950 ℃固溶+时效后的应力腐蚀敏感性变化小,800 ℃固溶+时效后的应力腐蚀敏感性先减小后增大。残余应力接近0(固溶温度为800 ℃时)的试样在较高Cl浓度下的应力腐蚀敏感性比残余应力水平较大试样低。高残余拉应力状态试样发生脆性断裂;随着残余应力降低,断口出现韧窝,当残余应力接近0或转变为压应力(固溶温度为950 ℃)时试样发生脆韧混合断裂。

       

      Abstract: Industrial pure iron specimens were formed by selective laser melting and subjected to solution at different temperatures (650, 800, 950 ℃) and aging at 400 ℃ to control residual stresses. The slow strain rate tensile test of the formed specimens was carried out in NaCl solution with different NaCl mass fractions (3.5%, 5.0%, 10.0%). The effect of residual stress on stress corrosion behavior of formed specimens was studied. The results show that the high residual tensile stress in the deposited (before solution + aging treatment) specimens enhanced its stress corrosion sensitivity at relatively high Cl concentration (mass fraction not less than 5.0%). With the increase of Cl concentration, the stress corrosion sensitivity of the deposited specimens increased. After solution and aging treatment, the residual stress decreased, the stress corrosion sensitivity decreased at relatively high Cl concentration. With the increase of Cl concentration, the stress corrosion sensitivity of specimens after 650,950 °C solution and aging treatment changed little,and the stress corrosion sensitivity of spcimens after 800 °C solation and aging trentment decreased first and then increased. The stress corrosion sensitivity of the specimens with residual stress close to zero (solution temperature was 800 °C) was lower at relatively high Cl concentration than those with relative high residual stresses. The tensile fracture of the specimens with a high residual tensile stress was brittle fracture. With the decrease of residual stress, dimples appeared on the fracture surface. When the residual stress was close to zero or transformed into compressive stress (solution temperature was 950 °C), the tensile fracture was brittle-ductile fracture.

       

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