镍基合金粉末光束堆焊层的微观组织及强化机理　

MICROSTRUCTURE AND STRENGTHENING MECHANISM OF Ni-BASED ALLOY POWDER SURFACING LAYER BY LIGHT BEAM

采用Ｘ射线衍射、ＳＥＭ、ＥＤＡＸ及显微硬度和洛氏硬度等分析手段研究了含碳量为１．０％ 的 ＮｉＣｒＢＳｉ系自熔合金粉末光束堆焊层的微观组织及强化机理．结果表明．采用光束镍基合金粉末堆焊可 在铁碳合金表面获得与基体冶金结合良好、无裂纹、轻度稀释的强化层.堆焊热输入对堆焊层稀释率及合金 元素烧损的影响程度决定了堆焊层微观组织及物相组成,小热输入堆焊时．堆焊金属轻度稀释（ｎ＝３.５％）， 其显微组织由少量初生的γ－Ｎｉ和大量的γ－Ｎｉ＋Ｎｉ３Ｂ＋Ｎｉ３Ｓｉ三相共晶组成的亚共晶基底．以及在基底 上分布着大量的 Ｃｒ２３Ｃ６、（Ｃｒ，Ｆｅ）７Ｃ３高硬度相组成：采用大热输入堆焊，堆焊金属稀释率达 １２％， 堆焊层由大量的γ－（Ｆｅ，Ｎｉ）枝晶和少量γ－（Ｆｅ，Ｎｉ）＋Ｍ７Ｃ３共晶组成．在堆焊层中未发现一次碳化物 的析出．在光束扮末堆焊层中大量高硬度 Ｍ２３Ｃ６、Ｍ７Ｃ３型碳化物和 Ｎｉ３Ｂ、Ｎｉ３Ｓｉ共晶相的析出以 及合金元素在γ相中的过饱和固溶是其得以强化的主要原因，与ＴＩＧ堆焊相比．采用相近热输入所获得 的光束粉末堆焊层的耐磨性提高了３倍以上。

The microstructure and strengthening mechanism of NiCrBSi system alloy powder (1.0 %C, mass fraction) surfacing layer by light beam heating were investigated by means of X-ray diffraction, SEM, EDAX, microhardness, Rockwell hardness, etc. The results showed that the light beam Ni-based alloy powder surfacing layer can be metallurgically bonded with the Fe-C alloy substrate. The surfacing layer has lower dilution and no cracks. The influence of heat input on dilution and burning loss of alloy elements determines the microstructure and the phase constitution of surfacing layer. When lower heat input is used, the microstructure of surfacing layer with lower dilution (η=3.5%) consists of high hardness phases (Cr23C6, (Cr,Fe)7C3) precipitated on hypoeutectic matrix composed of a little of primary γ-Ni and a lot of trinary eutectic of γ-Ni+Ni3B+Ni3Si. When higher heat input is used, the dilution of surfacing layer is as high as 12% and the surfacing layer consists of a lot of γ-(Fe, Ni) dendrite and a little of γ-(Fe, Ni)+M7C3 binary eutectic. There is no primary carbide in this kind of surfacing layer. The precipitation of carbide M23C6 and M7C3 and eutectic Ni3B and Ni3Si, and the oversaturated γ phase by alloy elements result in the strengthening of surfacing layer. Compared with TIG surfacing, the wear resistance of light beam surfacing layer is 3 times higher than that of TIG surfacing layer with the analogical heat input.