Elimination of laser direct forming crack on DD4 parts by induction heating

To solve the problem of cladding layer cracking of single-crystal Ni-based superalloy DD4 during the laser direct forming process, DD4 parts are fabricated on the directionally solidified DZ125L substrate by different processes. The kinds and the characteristics of cracks in cladding layers of DD4 parts and the effects of basic process parameters on the crack rate of DD4 parts are investigated. The laser direct forming process which is assisted by induction heating is proposed to eliminate the cladding layer cracks of DD4 parts. The results indicate that the cracks in the cladding layers of DD4 parts mainly include solidification crack and liquidation crack, and most of the cracks are the latter one. Reducing laser power, increasing scanning speed, and choosing appropriate overlapping space and elevation can decrease the crack rate of cladding layers of DD4 parts. The crack rate of the DD4 parts can be reduced to 0.230 mm·mm^-2 by optimizing process parameters. The crack rate of DD4 parts decreases with the elevation of the induction heating temperature, and the crack rate is 0.017 mm·mm^-2 when the induction heating temperature is 1200℃.