Si对625合金激光熔覆层高温氧化特性的影响

Effect of Si on High Temperature Oxidation Characteristics of Laser Cladding 625 Alloy

利用循环氧化法,研究了不同Si含量(0%,1%,3%,质量分数)的625合金熔覆层在700、800、900℃下氧化144 h后的高温氧化行为。用XRD分析了氧化物相。通过SEM/EDS研究了氧化物表面和截面的形貌、元素组成和氧化膜的厚度。结果表明,不同温度下试样的氧化动力学都保持抛物线规律,随着温度的升高,氧化增重逐渐增加。通过观察,在900℃时,0%Si含量的625合金熔覆层出现了氧化膜大面积剥落的情况,3%Si含量的合金熔覆层氧化膜保持完整。在700℃时,随着Si含量增加,氧化膜表面的氧化颗粒尺寸减小且更加致密,同时促进了Cr_(2)O_(3)氧化物的生成。在700℃下,0%Si含量的试样出现了大片的内氧化区域;1%Si含量的试样基体部分出现了2处条状的含Ni,Cr,Mo的氧化物相区;而3%Si含量的试样氧化后由于生成了富Si的内氧化层,这阻止了内氧化的发生。外层Cr_(2)O_(3)氧化膜和内层SiO_(2)的联合作用既阻止了O阴离子的渗入也抑制了Fe等金属离子的扩散,提高了合金熔覆层的抗氧化性。

The high temperature oxidation behavior of 625 alloy cladding layer with different Si contents was studied by cyclic oxidation method after 144 h oxidation at 700,800 and 900°C.The oxide phase was analyzed by XRD.The surface and cross section morphology,elemental composition and oxide film thickness were studied by SEM/EDS.The results show that the oxidation kinetics of the samples at different temperatures keep a parabolic law,and the oxidation mass gain increases gradually with the increase of temperature.The oxidation film of 0wt%Si 625 alloy cladding sample peels off in a large area at 900°C,while the oxidation film of 3wt%Si alloy cladding sample remains intact.With the increase of Si content at 700°C,the oxidation particles on the surface of the oxide film decrease in size and become denser,which promotes the formation of Cr_(2)O_(3).At 700°C,a large area of internal oxidation appears in 0wt%Si sample,there are two strip oxides containing Ni,Cr and Mo in the substrate of 1wt%Si sample,while the inner oxidation of 3wt%Si samples is prevented due to the formation of Si-rich inner oxidation layer.The combined effect of the outer layer of Cr_(2)O_(3) oxide film and the inner layer of SiO_(2) not only prevents the infiltration of O anions but also inhibits the diffusion of Fe and other metal ions,thus improving the oxidation resistance of the alloy cladding.