Wear Resistance of Multiphase Diffusion Carbide Coatings

Abstract

Multiphase diffusion carbide coatings of the types: M 7 C 3 ± VC, M 7 C 3 ±TiC and M 7 C 3 ±VC±TiC have been produced by pack cementation method on three tool steels at 1000 C during 6 h using 15 powder mixtures. Thickness of diffusion coatings varied in the range of 14±32 lm while hardness was in the range 2012±5150 HV0,05. Phase composition of coatings depended on type of powder mixture and a steel. Hardness of coatings increased with FeV and/or FeTi concentration in the mixture while metallic luster and surface finishing increased with FeCr content. The maximum wear resistance was achieved for M 7 C 3 ±VC±TiC coating formed in the mixture containing Ti, V, Cr in the mass proportion 4:4:2. Coatings of lower hardness, formed in Cr-rich mixtures worn mainly by microcutting and grooving while harder coatings formed in V-rich mixtures worn mainly by oxidation. Appearance of brown turnish on the surface of the latter coatings lowered the wear intensity. No difference in wear mechanism and intensity was found for the same type of coating formed on different steel matrix.The goal of diffusion metallizing (chromizing, vanadizing, titanizing) consists on producing strongly adherent corrosion and wear resistant coatings characterized generally by a high hardness. [1±3] Despite of an important progress in developing new methods and techniques of surface modification there are still demands for simple and cheap technologies. Diffusion pack cementation belongs to such methods, its modification brings quickly economical advantages. [4±6] The great advantage of this method is that ferroalloys, the main component of powders, are relatively cheap and easily accessible. Moreover a powder mixture can be used several times because ferroalloy grains of average size 60 lm are exploited only in several microns per process. The exploited layer of grains is then eliminated by barreling before next application.Mechanism of formation of monolayer carbide coatings on ferritic alloys is well known. It was found [5] that M 7 C 3 coating grew inward a steel due to external Cr diffusion while TiC or VC coating grew outward from the original surface due to carbon diffusion from a steel through the forming coating. [7,8] There is a lack of information in the literature on the formation of carbide layers by simultaneous diffusion of several carbide forming metals into Fe±C-rich alloys. Codiffusion of Cr and V into a low-C steel described in [9] leads to formation of solid solution coatings. Chromizing applied after vanadizing enabled to produce a two-layers coating: VC M 7 C 3.[10] Earlier investigations [11±12] proved that the chemical and phase composition as well as hardness of an individual layer could be varied in a relatively broad range by changing composition of powder mixture. It was shown [12] using FeV±FeCr± FeTi mixtures that both single phase and multiphase diffusion carbide coatings could be formed on steels. Multiphase coatings consist of carbide layers of different composition, Table 1. Compositon of tool steels used as matrix...

Diffusion Carbide Layers Produced on Tool Steel in Chromium Chloride Atmosphere at Low Pressure

“…A comparison was made between the layer thickness produced on the tool steel surface using the novel vacuum method and a traditional chromizing process by pack powder method at 850, 900, and 950°C within l0 h (Figs. [6][7][8]. The chromized carbide layer thickness, produced by means of the novel vacuum method, was about 30% greater than the layer produced by traditional pack powder method.…”

“…Diffusion chromizing is a thermochemical treatment employed today for improving properties of steel surfaces such as wear and corrosion resistance [1][2][3][4][5]. There is a lot of bibliographical data concerning the diffusion chromizing process, in particular, problems connected with hard carbide layers produced by the pack powder method, which are quite well expounded [6][7][8][9].…”

Estimation of Wear Resistance for Multilayer Coatings Obtained by Nitrogenchroming

“…Nitriding increases wear resistance and reduces the friction coefficient of stainless steel at normal and elevated temperatures [36,42,43]. Even though nitrided steels have 2-4 times less wear than cemented after hardening and low-temperature tempering, there are cases when the positive effect of nitriding on wear resistance is absent.…”

Manufacturing Process, Microstructure and Physico-Mechanical Properties of W-Cr Coatings Reinforced by Cr3C2 Phase Produced on Tool Steel through Laser Processing

“…In some attempts, primary phases are introduced directly in the form of carbide particles, while in others pure metal elements and carbon are introduced to produce carbides in situ. In light of the very good diffusion properties of surface layers obtained after diffusion chromium plating processes [ 18 , 19 , 20 ], it is reasonable to test whether the introduction of a reinforcing phase in the form of chromium carbide will also lead to high hardness and wear resistance.…”