摘 要:为了改善钛合金的硬度和耐磨性能,利用5 k W YLS-5000光纤激光器,在TC4合金表面分别激光熔覆纯Ti粉、Ti-15%(Mo+Si)和Ti-30%(Mo+Si)混合粉末(质量分数,Mo与Si原子比为1∶2),通过正交实验选择合适的功率和扫描速度等工艺参数,得到3种不同的涂层,利用金相显微镜(OM)、扫描电镜(SEM)对熔覆层的微观组织进行观察和研究、X射线衍射仪(XRD)研究熔覆层相组成,用显微硬度仪测得3种熔覆层的硬度。结果发现,功率为3 k W扫描速度10 mm·s-1得到熔合较好,缺陷较少的熔覆层。熔覆纯钛粉涂层组织为细小针状马氏体α’相,熔覆Ti-15%(Mo+Si)涂层在界面处共析出白色条状Ti Si2,熔覆Ti-30%(Mo+Si)涂层上部出现了镶嵌在涂层中的分块状Mo5Si3,MoSi2硬质相,而且白色晶间析出物增多,XRD结果显示β相增多。3种涂层熔覆区硬度有很大的区别,熔覆纯钛粉涂层平均硬度为HV0.2500左右,熔覆Ti-30%(Mo+Si)涂层最高硬度达到了HV0.21120,是基体的3.4倍左右。分析比较了3种涂层组织差异的原因,Mo,Si元素添加对钛合金组织的影响,结合热力学分析,探讨混合粉末形成Mo Si2的反应机制。
为了改善钛合金的硬度和耐磨性能,利用5 k W YLS-5000光纤激光器,在TC4合金表面分别激光熔覆纯Ti粉、Ti-15%(Mo+Si)和Ti-30%(Mo+Si)混合粉末(质量分数,Mo与Si原子比为1∶2),通过正交实验选择合适的功率和扫描速度等工艺参数,得到3种不同的涂层,利用金相显微镜(OM)、扫描电镜(SEM)对熔覆层的微观组织进行观察和研究、X射线衍射仪(XRD)研究熔覆层相组成,用显微硬度仪测得3种熔覆层的硬度。结果发现,功率为3 k W扫描速度10 mm·s-1得到熔合较好,缺陷较少的熔覆层。熔覆纯钛粉涂层组织为细小针状马氏体α'相,熔覆Ti-15%(Mo+Si)涂层在界面处共析出白色条状Ti Si2,熔覆Ti-30%(Mo+Si)涂层上部出现了镶嵌在涂层中的分块状Mo5Si3,MoSi2硬质相,而且白色晶间析出物增多,XRD结果显示β相增多。3种涂层熔覆区硬度有很大的区别,熔覆纯钛粉涂层平均硬度为HV0.2500左右,熔覆Ti-30%(Mo+Si)涂层最高硬度达到了HV0.21120,是基体的3.4倍左右。分析比较了3种涂层组织差异的原因,Mo,Si元素添加对钛合金组织的影响,结合热力学分析,探讨混合粉末形成Mo Si2的反应机制。
Microstructure of Ti-Mo-Si Coating Laser Cladding on Titanium Alloy
Zheng Liang Li Dong He Congcong Chen Qianqian Deng Zenghu Tong Shaohui
School of Materials Engineering,Shanghai University of Engineering Science
Abstract:
In order to improve the hardness and wear resistance of titanium alloys,Ti,Ti-15%( Mo + Si) and Ti-30%( Mo + Si)( mass fraction) were cladded on titanium alloy using 5 kW YLS-5000 fiber lasers. Selecting appropriate power and scanning speed through orthogonal experiment,three different coatings were got. Using optical microscopy( OM) and scanning electron microscopy( SEM),the microstructure of cladding coatings were observed and studied. X-ray diffraction( XRD) was used to study the phase composition of cladding layer,and the hardness of three cladding layers was measured by micro hardness tester. The results showed that preferably fused,less defective cladding layer was obtained with the power of 3 kW and the scanning speed of 10 mm·s~(-1). It showed that small acicular martensite α' phase appeared in cladding titanium powder coating,white strip TiSi_2co-precipitated at the interface of Ti-15%( Mo + Si) cladded coating,an upper scoring mosaic block Mo5Si3 and MoSi_2 hard phase appeared in Ti-30%( Mo + Si) cladded coating,and increasing inter-white crystals precipitated in the coating. XRD result displayed that β phase increased. The hardness of cladding region of the three coatings was very different,and the average hardness of titanium powder cladded coating was about HV0. 2500,Ti-30%( Mo + Si) cladded coating reached the maximum hardness HV0. 21120,which was 3. 4 times that of the matrix. The differences between the three coatings and the impact of Mo,Si alloy elements added on the microstructure were analyzed and compared. Combined with thermodynamic analysis,the reaction mechanism for the formation of the mixed powder of MoSi_2 was explored.
图2 基体和3种涂层的XRD分析Fig.2 XRD patterns of substrate and coatings
2.3熔覆层组织分析
图3为涂层横截面显微组织,图3(a)为熔覆层宏观图,右侧为预置粉末2激光功率3 k W扫描速度10 mm·s-1的熔覆层,可以看出涂层成型良好,表面有略微氧化的现象,左侧为其工艺参数下搭接率为70%的搭接涂层,搭接4道。图3(b)为熔覆层的横截面全貌,可以看出涂层与基体结合良好,涂层也出现了气孔,还有未熔颗粒聚集在一块。图3(c)可以看出涂层表面呈细密的针状,组成类似网篮的组织,晶界不完整且呈锯齿状,与基体的熔合较好,根据Ti的相图和激光熔覆的加热冷却规律推断,Ti高温熔化在低温下快速冷却,由高温β相发生马氏体相变,转变为低温的针状马氏体α'组织,结合XRD衍射进一步确定针状组织为{334}型马氏体α'组织,在β相转变基体上形成并交错编织成网篮状,并且出现了二次枝晶。图3(b)为激光熔覆粉末2涂层组织,涂层与熔合线清晰,熔合线以上的重熔区出现了沿温降方向生长的树枝晶,大约150μm左右;涂层区为花瓣状枝晶,枝晶臂约为50μm,枝晶间隙弥散分布着细小的白色条状析出物。图3(e)为激光熔覆粉末3混合涂层,涂层主要为花瓣状枝晶和白色的基底,与图3(d)相比枝晶晶粒变细小,白色基底变多,基底模糊的晶界分隔开。
图3 激光熔覆涂层横截面组织Fig.3 Macrostructure and SEM images of microstructure of laser cladding coatings
(a)Macroscopic diagram of Coating 2;(b)Cross section of Coating 2;(c)Coating 1;(d)Coating 2;(e)Coating 3;(f)Upper of Coating 3