Laser cladding of composite powders

The protection against abrasive wear requires high hardness of the loaded surface. In many cases transformation hardening of steels is insufficient, and a hardfacing process is necessary. For coatings produced in this manner, wear is governed by the content of hard intermetallic or carbidic phases and their grain size. The abrasive wear resistance is higher for larger content and size of hard phases. Also the hard phases must be harder than the abrasive particles. Laser cladding with continuous powder feed into the melting pool permits the deposition of heterogeneous alloys with uniformly distributed nonmelted or nearly nonmelted hard particles in a metallic matrix. The present investigation shows that hard particle contents up to 40 percents of volume can be reached experimentally. On the base of various material systems, e.g. WC/Co-NiBSi, WC-Stellite 21 and TiC-austenitc steel, metallurgical aspects of matrix embrittlement due to the hard particle dissolution are discussed. The techn ological conditions for a low carbide dissolution are specified and results of wear tests are presented.