摘要
以316L不锈钢粉末为原料,采用激光熔覆技术以单向扫描和往复扫描两种方式在AISI304不锈钢表面进行多层多道熔覆,研究了熔覆层的组织以及熔覆层中的残余应力,并进行了有限元模拟。基于316L不锈钢粉末的激光熔覆层截面形貌,利用ABAQUS有限元软件建立复合热源模型,分别计算熔覆层的温度场及应力场。对熔覆层中的残余应力σ_(x)和σ_(y)进行测试,测试结果与模拟计算结果吻合得较好,验证了有限元模型的可靠性。温度场模拟结果表明,往复扫描路径下的热累积大于单向扫描路径下的热累积。结合温度场结果与微观组织分析了单向扫描路径下熔合线处的晶粒尺寸相比往复扫描路径下更均匀的机理。基于温度场结果分析了熔覆层中的应力分布规律以及往复扫描路径下的熔覆层应力大于单向扫描路径下的机理。
Objective During the laser cladding process,the heat input of the laser heat source is not uniform,which will cause an uneven temperature field.The residual stress produced by the uneven temperature field will increase the crack tendency and affect the size,structure,and performance of the cladding layer,thereby considerably reducing the quality of the specimen.The cladding scanning method will affect the heat conduction and accumulation,thus affecting the stress and deformation of the work piece.Furthermore,the heat accumulation of the laser heat source considerably influences the morphology of the solidified structure of the cladding layer.An improved scanning method can produce a small heat-affected zone,stress,deformation and a fine and more uniform microstructure when using the same process parameters of laser cladding,thereby improving the manufacturability of laser cladding.The internal temperature change of the molten pool is difficult to measure using the existing test methods.Using numerical simulations to study the temperature and stress fields in the laser cladding process can greatly reduce the experimental cost and time.The temperature and stress field simulation results can be used to explain the influence of different scanning strategies on the characteristics of the cladding solidification structure and the distribution of residual stress.Methods AISI304 stainless steel and 316 L stainless steel powder are used in this study.The 316 L stainless steel coating is fabricated on the surface of AISI304 stainless steel via coaxial powder feeding laser cladding using codirectional and reciprocating scanning methods.Then,the cladding layer is sampled for metallographic analysis.The metallographic corrosion solution is the Fe Cl3 hydrochloric acid ethanol solution.Furthermore,the temperature and stress fields in the laser cladding process under different scanning strategies are calculated using the finite element simulation software ABAQUS.The influence of scanning strategies on the temperature and stress field distributions is studied.Finally,to verify the simulation results,the residual stress in X and Y directions of the cladding layer is analyzed using an i XRD residual stress analyzer.Results and Discussions Heat accumulates in the laser cladding process.The peak temperature of the cladding layer under the reciprocating scanning path is considerably higher than that under the codirectional scanning path,and the heat accumulation of the cladding layer under the reciprocating scanning path is more severe(Fig.8).As the cladding of the first two layers preheats the cladding of the third layer,the temperature gradient and cooling rate in the bonding zone of the second and third layers are less than those in the bonding zone between the bottom cladding layer and the matrix(Fig.10);hence,the grain size of the third cladding layer is larger than that of the first cladding layer(Fig.9).Compared with reciprocating scanning,the grain size of the cladding layer under codirectional scanning is smaller and the microstructure is more uniform(Fig.9).The Mises stress in the reciprocating scanning path is greater than that in the codirectional scanning path,and the maximum residual stress is located at the junction between the cladding layer and the matrix at the beginning of the heat source scanning(Fig.13).The distribution law of residual stressesσ_(x) andσy of the cladding layer under the codirectional and reciprocating scanning paths is similar.The tensile stress of the work piece is located on the substrate adjacent to the cladding layer,and the compressive stress is located on the substrate far away from the molten pool.The distribution position of the tensile and compressive stresses is relatively vertical(Figs.14 and 15).Conclusions In this study,the 316 L stainless steel powder is cladded on the surface of AISI304 stainless steel using laser cladding technology.The microstructure and residual stress of the cladding layer are studied,and a finite element simulation is performed.The codirectional and reciprocating scanning methods are used for multi-layer and multi-pass cladding.Based on the cross-section morphology of the 316 L laser cladding layer,the composite heat source model is established using the finite element simulation software ABAQUS,and the temperature and stressfields are calculated.The test results of the residual stressesσ_(x) andσy of the cladding layer show good agreement with the simulation results,thus verifying the reliability of the finite element models.The temperature field simulation results show that a larger amount of heat is accumulated using the reciprocating scanning method than using the codirectional scanning method.By combining the temperature field results and microstructure morphological results,the grain size of the cladding layer using the codirectional scanning method is more even than that using the reciprocating scanning method.The stress distribution of the cladding layer and the stress mechanism in the reciprocating scanning method is better than those in the codirectional scanning method based on the temperature field results.The tensile stress of the residual stressesσ_(x) andσy on the work piece is located on the cladding layer and the substrate close to the cladding layer.The compressive stress is located on the substrate with a vertical distribution relative to the tensile stress.
作者
吴俣
马朋召
白文倩
陈静青
Wu Yu;Ma Pengzhao;Bai Wenqian;Chen Jingqing(Key Laboratory of Advanced Technologies of Materials,Ministry of Education,School of Materials Science and Engineering,Southwest Jiaotong University,Chengdu Sichuan610031 China)
出处
《中国激光》
EI
CAS
CSCD
北大核心
2021年第22期12-23,共12页
Chinese Journal of Lasers
基金
国家自然科学基金(51504198,51474178)
中央高校基本科研业务费专项资金项目(A0920502051820-48)。
关键词
激光技术
激光熔覆
有限元仿真
316L不锈钢
温度场
应力场
laser technique
laser cladding
finite element simulation
316L stainless steel
temperature field
stress field
