Current state of the scientific problem of wc – co hard alloys surface hardening (Review)

Abstract

The article presents the review of Russian and foreign researches on surface hardening of WC – Co hard alloys aiming at increasing their wear-resistance. There is a great reserve of increasing wear-resistance and operational durability of hard-alloy products in application of surface methods of hardening using different coatings and coating with basic structural components of up to 100 nanometers. The most widely spread coatings on WC – Co hard alloys are coatings made from TiC, TiN providing high energy lattice ties, high flowing temperature and hardness. Use of TiC, TiN as surface layers on hard-alloy tools results in reduction of friction coefficient in pair with steel in 1.5 – 2.0 times, but use of TiN + ZrN ionic-plasma coatings reduces friction coefficient in 5.9 times in comparison with the initial condition. Today multilayer coatings are very popular. The most widely spread are coatings of TiN + TiC and Al2O3 + TiC. Their surface wear is directly proportional to the coating thickness. Combined multilayer coatings described above are not the final solution to the problem of increasing wear resistance of hard alloys. The research projects are carried out in our country that are based on theoretical possibilities for obtaining strength of the hard alloy gradually from viscous and high-strength core to wear-resistant surface. The FSUE VNIITS has developed a method for obtaining alloys with variable content of cobalt along the plate thickness. Due to this, it is possible to vary composition of alloys along the thickness of sample, from VK20 to VK2, as a result working part of plate has wear resistance equal to VK2 alloy, and the base endures significant bending stresses. Recently different cutting tools with diamond coatings on hard alloys have been used in Russia and all over the world. To increase the service life of hard-alloy plates of VK group, methods of hardening using concentrated energy flows are used. Among them there are hard alloys’ surfaces treatment by γ-quanta, ion beams, laser beams; electro-explosive alloying, electro-erosion hardening by alloying etc.