Mechanical properties and characterization of metallic bond coat used in hardfacing of petroleum drill bits
Y. Yahmi1, D. Miroud2, B. Maamache1 & R. Badi1 y.yahmi@csc.dz
1Welding and NDT Research Center, BP 64, Cheraga, Algiers, Algeria
2Faculty of Mechanical Engineering and Engineering Processes, University of Science and Technology Houari Boumediene, Bp 32 El Alia 16111 Bab Ezzouar Algiers Algeria
Abstract:
Tungsten carbides are widely used as weld hardfacing deposits in petroleum drill bits. To assure proper bonding of the hardfacing to the substrate, several choices of bond coating layers are offered.
In this study, tow different commercial powders A and B and mixtures of both them were thermal sprayed onto a carbon steel XC18 substrate used in petroleum drill bits. The micro hardness respectively, of the hardfacing surface and bond coating layers was measured. The microstructure was observed by optical microscopy and field emission scanning electron microscope equipped with energy-dispersive X-ray spectrometry.
It has been observed that the mixture of 75% of A and 25% of B produces an uniform coating metallurgically bonded to the substrate with a little heat affected zone and a little amount of porosity.
Keywords: Thermal spray coating, drill bit, Bond coat layer, weld hardfacing, Adhesion;
1. Introduction
Combination of desirable properties is met in multiphase materials, including carbide composites (hardmetals and cermets). Composites are prospective for use under the conditions of two or more bodies interacting, e.g. tribological applications. Tungsten carbide base hardmetals are the most widely used materials for different wear applications owing to their excellent combination of high wear resistance and strength-toughness [1,2]. Major applications of tungsten carbide based hardmetals cover metal removal cutting tools, rock- and earth drilling tools and sheet metal forming tools [2].
Bond coats play a significant role in manipulating the stability of tungsten carbides (WC) coatings deposited on steels. In this study, tow different commercial bond coat powders (A, B and A+B) were prepared on ordinary steel used for drill bits (XC 18) by oxyacetylene spraying. The spraying behavior of the powders, the microstructure of the produced bond coats were investigated to find the positive bond coat for WC harfacing. Results indicate that the composition and structure of original powders affect the structure and properties of the sprayed bond coats. For the candidate bond coats, the (75% A+25% B) bond coat is demonstrated as the most appropriate one for WC deposited on XC 18 steel substrate, which is mainly attributed to its straight interface line having only a few pores and free of cracks and good adhesion with the substrate.
