Microstructure of bonding zones in laser-clad Ni-alloy-based composite coatings reinforced with various ceramic powders
- PDF / 4,808,706 Bytes
- 10 Pages / 597.28 x 777.28 pts Page_size
- 54 Downloads / 173 Views
I.
INTRODUCTION
THE interracial fusion bonding between laser-clad coatings and their substrates is a characteristic feature of the laser-cladding technique differing from other surface modification methods. Such bonding can be produced either by comelting a preplaced coating and a thin layer of the substrate or by powder injecting reinforcing particles into the laser-melt pool of the substrate. Depending on the factors governing the solidification of the laser-melt pool, the microstructural feature of the interracial bonding and the mechanism of its formation are changeable in different composite systems of the clad material. Frenk and Kurztq presented several theoretical models to describe the formation of microstmcture in laser surface alloying. Starting with the local growth conditions, they introduced the concept of microstructure selection and gave a limited discussion about the microstructure of the bonding zone (BZ). Atamert and Bhadeshiat21 observed the formation of plate martensite zone near the fusion boundary. Such martensite with a body-centered tetragonal crystalline structure is known to be detrimental since its formation is associated with internal stress, which adversely influences the cohesion of the coating to the substrate. De Damborenea and Vazquez [3] have found a good metallurgical bond between the NiCrA1 coating and 316L steel substrate using the powder injection technique. However, the addition of zirconia particles to the NiCrA1 coating probably induced
intergranular cracks, although the incorporation of the particles was designed to reinforce the coating. Even though these earlier studies have paid attention to the structural feature of the BZ, the mechanism of its formation has not been well established and, especially, the effect of ceramic particles on the interfacial bonding is unclear. So, further study is needed in this respect. This article reports the results of microstructural investigation and the formation mechanism of the BZs in four kinds of composite coatings, i.e., Ni-alloy coating without reinforcement and reinforced by nitride, carbide, or oxide ceramic particles, respectively. The main purpose of this study is to examine the effect of ceramic particles on the interfacial bonding of the coatings in which a partial dissolution (TIN), complete dissolution (SIC), or immiscible melting (ZrO2) of the particles takes place during laser cladding. II.
EXPERIMENTAL PROCEDURE
A. Materials for Investigation The laser-clad composite coatings studied were based on a Ni-Cr-B-Si alloy reinforced with 30 vol pct SiC, 30 vol pct TiN, or 60 vol pct ZrO2 (partially stabilized with 4 tool pct Y203), respectively. The commercial steel 1045 was used as a substrate for TiN or SiC reinforced wear-resistant coatings, and stainless steel 4Cr13 was used as a substrate Table I. Chemical Composition (Weight Percent) of Substrate Steels and the Coating Matrix Ni Alloy
Y.T. PEI, Associate Professor, is with the Department of Materials Science and Engineering, Beijing Polytechnic University, Beijin
Data Loading...
