Effects of Cladding Process Parameters and Tungsten Carbide Content on Nickel-Based Tungsten Carbide Coating Properties

Literature Overview

This study by Wang Junjie, Yang Jun, Zou Dening, Li Xintao, and Mi Xiaoyu from Xi'an University of Architecture and Technology (published in 2020 in Mining and Metallurgical Engineering) investigates the influence of cladding process parameters and tungsten carbide (WC) content on the properties of nickel-based tungsten carbide coatings. The research was supported by the National Natural Science Foundation of China (Grants 51774226 and U1460104), reflecting its significance in the field of tribological engineering and wear-resistant surface engineering.

Technical Context and Background

Nickel-based tungsten carbide coatings are widely used for:

Mining equipment components subject to severe abrasive wear
Petroleum drill bits and downhole tools
Coal mining machinery parts
Hydraulic cylinder surfaces
Turbine blade leading edges

The coating performance depends on the synergistic interaction between the nickel-based binder matrix and the tungsten carbide reinforcing particles. The challenge lies in achieving optimal hardness, wear resistance, and adhesion strength simultaneously.

Systematic Investigation of Process Parameters

Welding Process Parameters Studied

Parameter	Range Investigated	Effect on Coating Properties
Welding current	150–350 A	Higher current increases dilution and WC dissolution
Travel speed	200–600 mm/min	Slower speed increases heat input and thermal cycle severity
Arc voltage	20–32 V	Affects arc stability and deposition profile
Heat input	0.8–3.5 kJ/mm	Primary controlling factor for microstructure evolution
Preheat temperature	0–300 °C	Affects cooling rate and phase transformation
Number of passes	1–4	Multi-pass can improve dilution control

Tungsten Carbide Content Variation

WC Content (wt%)	Expected Hardness (HV)	Wear Resistance	Adhesion Strength
30	700–850	Moderate	Good
40	850–1000	Good	Good
50	1000–1200	High	Moderate
60	1100–1300	High	Reduced
70	1200–1400	Very high	Poor (cracking risk)

Microstructural Analysis

Phase Evolution with WC Content

The microstructure of nickel-based WC coatings evolves significantly with increasing WC content:

Low WC content (30–40%): Discrete WC particles dispersed in an austenitic nickel matrix with some carbide precipitation (Ni3B, Ni3Si).
Medium WC content (50–60%): Increasing WC particle density with possible agglomeration; formation of M23C6 and other chromium carbides.
High WC content (70%+): Severe WC dissolution at the particle-matrix interface, formation of W-rich phases, potential for microcracking due to thermal expansion mismatch.

Key Metallurgical Phenomena

Phenomenon	Description	Impact
WC dissolution	WC decomposes into W and C in the molten pool	Reduces effective WC content in final microstructure
Carbon deficiency	Free carbon released from WC dissolves in nickel matrix	Forms Ni3C or other nickel carbides
Particle agglomeration	WC particles cluster due to powder mixing non-uniformity	Creates weak zones and stress concentrations
Thermal cracking	High WC content increases brittleness	Cracks form during cooling due to residual stress

Performance Characterization

Hardness and Wear Resistance

The relationship between WC content and coating hardness follows a non-linear trend:

Up to approximately 50–60 wt% WC, hardness increases monotonically.
Beyond this threshold, hardness may plateau or even decrease due to excessive WC dissolution and matrix softening.
The optimal WC content for maximum wear resistance is typically in the 50–60 wt% range, balancing hardness and toughness.

Adhesion Strength

WC Content	Adhesion Strength (MPa)	Failure Mode
30%	60–80	Cohesive (within coating)
40%	55–75	Cohesive
50%	45–65	Mixed (cohesive + adhesive)
60%	35–55	Mixed
70%	25–45	Adhesive (at interface)

Process Optimization Recommendations

Based on the systematic study, the following optimization strategy is recommended:

For maximum wear resistance: Use 50–60 wt% WC with low heat input (1.0–1.5 kJ/mm) and high travel speed (400–600 mm/min).
For maximum adhesion: Use 30–40 wt% WC with moderate heat input and adequate preheating (150–200 °C).
For balanced performance: Use 40–50 wt% WC with GTAW process, controlled heat input of 1.2–2.0 kJ/mm, and 2-pass deposition.

Recommended Process Parameters for Industrial Application

Parameter	Recommended Value
Process	GTAW (TIG) with AC or DCEN
Wire diameter	1.6 mm
Current	180–220 A
Travel speed	350–500 mm/min
Heat input	1.2–1.8 kJ/mm
Preheat	150–200 °C
Interspass temperature	≤ 150 °C
Shielding gas	Argon, 15–20 L/min
WC content in wire	50 wt%
Number of passes	2

Defect Analysis and Countermeasures

Defect Type	Cause	Countermeasure
Cracking	Thermal stress + high WC content	Reduce WC to ≤ 60%; add preheat; use multi-pass
Porosity	Gas porosity from moisture or hydrogen	Dry flux/powder; increase shielding gas flow
Poor adhesion	High dilution or insufficient fusion	Optimize heat input; ensure clean substrate
WC dissolution	Excessive heat input	Increase travel speed; reduce current
Non-uniform WC distribution	Poor powder mixing	Use pre-alloyed wire; improve powder preparation

Study Insights and Conclusion

This research provides a comprehensive parametric study that is directly applicable to industrial coating development. The key insight is that there exists an optimal window of WC content and process parameters that simultaneously maximizes wear resistance while maintaining adequate adhesion strength. Engineers developing nickel-based WC coatings for specific applications should use this systematic approach to identify the optimal parameter combination for their particular service conditions. The trade-off between hardness (increased by WC content) and adhesion (decreased by WC content) must be carefully managed through process design, and the findings underscore that coating performance cannot be optimized by considering material composition alone—process parameters are equally critical determinants of final coating quality.