Microstructure and Wear Properties of Nickel-Based Alloy Plasma Surfacing Deposits

Literature Overview

Published in Hot Working Technology (Volume 42, Issue 3, 2013, pp. 151-155) by Hu Jianjun, Chen Guoqing, Li Shan, and Zhou Wenlong from Dalian University of Technology, this paper compares the microstructure, hardness, and wear performance of three commercially available nickel-based alloy powders (Ni40A, Ni50A, and Ni60A) plasma surfaced onto 1Cr18Ni9Ti stainless steel substrates. The research is supported by the Jiangxi Provincial Natural Science Foundation and the National 973 Program, reflecting the strategic importance of advanced surfacing technologies for China's manufacturing sector.

Alloy System Comparison

The three nickel-based alloys represent different compositions and performance targets:

Alloy Designation	Typical Composition	Primary Application
Ni40A	Ni-40Cr-Fe balance	General wear resistance, moderate hardness
Ni50A	Ni-50Cr-Fe balance	Enhanced wear resistance, higher hardness
Ni60A	Ni-60Cr-Fe balance	Maximum wear resistance, highest hardness

The numerical designation approximately corresponds to the chromium content, which is the primary variable influencing the type and quantity of hard phases formed during solidification.

Microstructural Characterization

All three surfacing deposits share a common feature: the base matrix is austenitic (γ-Ni), which provides good toughness and corrosion resistance. The critical differences lie in the precipitated phases:

Alloy	Precipitated Phases	Phase Characteristics
Ni40A	Cr7C3, M23C6, Ni3Si	Carbides with moderate hardness, fewer borides
Ni50A	CrB, M23(C,B)6, Cr7C3, Cr5B3, Ni3Si	Mixed carbides and borides, increased complexity
Ni60A	CrB, M23(C,B)6, Cr7C3, Cr5B3, Ni3Si	Similar to Ni50A but with higher volume fraction of hard phases

The progression from Ni40A to Ni60A shows increasing complexity and volume fraction of precipitated phases, particularly boride phases (CrB, Cr5B3) which become more prominent at higher chromium levels.

Performance Comparison

Property	Ni40A	Ni50A	Ni60A
Microhardness	Moderate	Higher	Highest (780 HV)
Wear resistance	Lowest	Intermediate	Highest
Friction coefficient	Lower	Lower	Highest
Matrix toughness	Best	Good	Moderate

The wear resistance ranking of Ni60A > Ni50A > Ni40A is consistent with the increasing volume fraction and hardness of precipitated phases. The higher friction coefficient of Ni60A is a direct consequence of its higher hardness and the presence of hard boride and carbide particles that increase surface roughness and mechanical interlocking during sliding contact.

Metallurgical Analysis

The formation of different precipitate types across the three alloys can be explained by the thermodynamic stability of various phases at different chromium concentrations:

At lower chromium (Ni40A) — Cr7C3 is the dominant carbide phase, forming at relatively lower chromium concentrations. M23C6 also forms as a chromium-rich carbide. Ni3Si forms as a silicon-rich intermetallic.
At intermediate chromium (Ni50A) — Boride phases begin to form as chromium concentration reaches levels where CrB and Cr5B3 become thermodynamically stable. The M23(C,B)6 phase represents a mixed carbide-boride structure.
At higher chromium (Ni60A) — Similar phase types to Ni50A but with higher volume fractions due to greater supersaturation of carbide and boride-forming elements. The increased chromium content drives more complete precipitation of hard phases.

Engineering Selection Guidelines

Based on the comparative analysis, the following selection guidelines emerge for different application scenarios:

Application Requirement	Recommended Alloy	Rationale
Maximum wear resistance	Ni60A	Highest hardness and wear resistance
Moderate wear with lower friction	Ni40A or Ni50A	Lower friction coefficient
Combined wear and corrosion	Ni50A or Ni60A	Austenitic matrix maintains corrosion resistance
Impact loading present	Ni40A	Better toughness from lower hard phase fraction
High-temperature service	Ni50A or Ni60A	Chromium-rich phases maintain stability

Process Optimization Considerations

Plasma surfacing parameters that influence the final properties of nickel-based alloy deposits include:

Current and voltage — Affect heat input, dilution, and cooling rate
Powder feed rate — Must be matched to thermal energy for complete melting
Travel speed — Controls heat input per unit length
Layer thickness — Multiple thin layers produce finer microstructures
Interlayer temperature — Affects the thermal history and phase transformation

For nickel-based alloys, lower dilution is particularly important because the substrate (1Cr18Ni9Ti in this study) has a significantly different composition. Excessive dilution would alter the phase balance and reduce the effectiveness of the surfacing treatment.

Study Insights

This comparative study provides engineers with a clear framework for selecting among nickel-based plasma surfacing alloys based on specific performance requirements. The Ni60A alloy, with its microhardness of 780 HV and superior wear resistance, represents the highest performance option for applications where wear is the dominant failure mode. However, the higher friction coefficient is a trade-off that may be unacceptable in applications where low-friction sliding is critical. The Ni40A alloy offers a more balanced combination of wear resistance, friction characteristics, and toughness, making it suitable for applications involving moderate wear with some impact loading. Understanding the phase evolution with chromium content enables rational alloy selection rather than empirical trial-and-error approaches. For engineers upgrading existing stainless steel components with nickel-based surfacing, this work provides the metallurgical basis for making informed decisions about alloy selection and process optimization.