Heat Treatment Effects on Abrasive Wear Resistance of Ni45 Powder Surfacing Deposits

Literature Overview

This study, authored by Qu Qi from Harbin Turbine Group Corporation and published in 2005 in Coal Mine Machinery (煤矿机械), Vol. 26, No. 3, pp. 81-83, investigates the influence of various heat treatment regimes on the abrasive wear resistance of Ni45 powder surfacing deposits. The research addresses a critical engineering challenge in mining and power generation equipment, where components subjected to severe abrasive wear conditions require optimized surface treatments to extend service life.

Core Technical Findings

The investigation systematically examined three categories of heat treatment effects on Ni45 powder surfacing deposits:

The Ni45 powder, a nickel-based alloy containing approximately 45% nickel with iron, chromium, and molybdenum as additional alloying elements, is known for its excellent abrasive wear resistance. The study confirmed that the combination of 950°C water quenching followed by 500°C tempering for 2 hours yielded the optimal wear resistance performance.

Interpretation of Technical Points

Metallurgical Basis for Heat Treatment Optimization

Ni45 powder deposits, when applied through thermal spray or powder surfacing processes, typically exhibit a microstructure consisting of a nickel-rich matrix with dispersed iron-rich carbide particles. The heat treatment at 950°C serves to homogenize the microstructure and potentially refine the carbide distribution. Water quenching from this temperature produces a martensitic or semi-martensitic transformation in the iron-rich regions, significantly increasing hardness.

The subsequent tempering at 500°C for 2 hours serves a dual purpose: it relieves internal stresses introduced during quenching while maintaining a favorable balance between hardness and toughness. The selection of 500°C is particularly significant because it falls within the range where secondary hardening may occur in some nickel-iron alloys due to the precipitation of fine carbides, contributing additional wear resistance.

Wear Mechanism Analysis

The ΔG-t relationship curves provide insight into the wear behavior of the Ni45 deposits under different heat treatment conditions. Typically, these curves exhibit three distinct stages:

1. Run-in period: Initial rapid wear as surface asperities are removed and a stable contact pattern is established.
2. Steady-state wear: Linear wear rate indicating a consistent material removal mechanism.
3. Accelerated wear: Sudden increase in wear rate as subsurface damage accumulates and material failure occurs.

The optimal heat treatment condition (950°C water quench + 500°C temper for 2 hours) likely minimizes the run-in period, maintains a low steady-state wear rate, and delays the onset of accelerated wear.

Tempering Temperature Sensitivity

The variation of tempering temperature reveals a characteristic hardness-wear resistance relationship. At lower tempering temperatures, the deposit retains higher hardness but may be more susceptible to brittle fracture under abrasive conditions. At higher tempering temperatures, toughness increases but hardness decreases, potentially reducing abrasion resistance. The 500°C tempering temperature represents an optimal compromise for the specific wear conditions tested.

Engineering Practice Integration

In coal mining machinery and power generation equipment, Ni45 powder surfacing is extensively applied to:

• Crusher hammers and jaws
• Rotary kiln liners
• Slurry pump impellers
• Conveyor roller surfaces
• Coal mill classifier blades

The heat treatment protocol identified in this study can be directly implemented in manufacturing workflows. For large components where full-furnace heat treatment is impractical, induction hardening or flame hardening can be adapted to replicate the 950°C austenitization followed by controlled cooling and tempering.

Process Implementation Considerations

When applying these findings to production environments, several factors must be considered:

• Distortion control: Water quenching from 950°C can cause significant distortion in thick or asymmetric components. Preheating and controlled quenching media (e.g., polymer quenchant) may be necessary.
• Scale formation: The high austenitization temperature promotes oxide scale formation, which may require post-treatment cleaning.
• Residual stress management: The quenching process introduces residual stresses that, if not properly relieved through tempering, can compromise the component's dimensional stability and fatigue performance.

Key Questions and Reflections

A notable limitation of this study is the relatively narrow range of test conditions examined. In practical applications, the wear environment varies significantly—dry sliding, lubricated sliding, three-body abrasion, and erosive wear all demand different material responses. The optimal heat treatment for one wear regime may not be optimal for another. Furthermore, the study does not address the effect of multiple thermal cycles on the long-term stability of the Ni45 deposit microstructure, which is particularly relevant for components operating at elevated temperatures.

The finding that 500°C tempering for 2 hours is optimal raises the question of whether shorter tempering times at slightly higher temperatures could achieve comparable results with reduced processing costs. This would be a valuable optimization direction for industrial implementation.

Study Insights and Implications

This research provides a clear, practical heat treatment protocol for maximizing the abrasive wear resistance of Ni45 powder surfacing deposits. The identification of 950°C water quench followed by 500°C tempering for 2 hours as the optimal condition offers engineers a straightforward guideline for production implementation. The systematic approach of examining cooling rate, tempering temperature, and tempering time independently demonstrates good experimental design methodology. For engineers working on mining equipment and power generation components, this study validates the importance of post-deposition heat treatment in achieving the full wear resistance potential of Ni45-based surfacing systems.