Microstructure and Abrasive Wear Performance of Cladding Alloys Containing In-situ Carbide Particles

Literature Overview and Background

In-situ formed carbide particles represent a promising approach to enhancing the abrasive wear resistance of weld overlay alloys. Unlike ex-situ reinforced composites that require separate particle introduction, in-situ carbides form directly during the solidification of the weld pool through controlled alloy chemistry. The literature reviewed here investigates Fe-Cr-C-Ni alloy systems designed to produce in-situ M7C3, Cr7C3, and (Cr,Fe)7C3 carbide particles during welding, and evaluates their microstructure, hardness, and abrasive wear performance against conventional wear-resistant overlay materials.

The concept of in-situ reinforcement offers several advantages: the carbide particles are inherently well-bonded to the matrix (no interface debonding), their size and distribution can be controlled through alloy composition and process parameters, and no expensive external reinforcement materials are required. The challenge lies in achieving sufficient carbide volume fraction while maintaining matrix toughness.

Core Technical Content

Alloy Design and Carbide Formation Thermodynamics

The study examines alloy compositions in the Fe-Cr-Ni-C system with varying carbon (1.5-4.0 wt%), chromium (12-25 wt%), and nickel (0-15 wt%) contents. The thermodynamic driving force for carbide formation is governed by the Gibbs free energy of precipitation:

• M7C3 (Fe,Cr)7C3: Forms preferentially at high carbon and moderate chromium
• Cr7C3: Dominates at high chromium (>18 wt%) and moderate carbon
• Ni3C: Forms in nickel-rich compositions but is metastable
• M23C6: Precipitates at grain boundaries during cooling

The optimal composition window for maximizing in-situ carbide formation is identified as: C = 2.0-3.5 wt%, Cr = 15-22 wt%, Ni = 5-12 wt%. Within this range, carbide volume fractions of 30-55% can be achieved, providing significant hardening effect.

Microstructure Characterization

The literature presents detailed metallographic and SEM-EDS analysis of overlay layers from different alloy compositions:

The nickel addition promotes austenite stabilization, which increases toughness but reduces the volume fraction of hard carbide phases. The trade-off between hardness (favored by high carbon and chromium) and toughness (favored by nickel and retained austenite) is the central metallurgical challenge addressed in this study.

Abrasive Wear Performance

Wear testing was conducted using standard dry sliding abrasion tests (ASTM G65 or equivalent) with SiC abrasive paper and three-body abrasion tests with quartz sand slurry. The results demonstrate clear trends:

The data confirms that higher carbide volume fraction and hardness correlate with improved wear resistance. However, the Fe-22Cr-3.5C composition, while achieving the highest wear resistance, exhibits reduced fracture toughness that may limit its applicability in impact-abrasive service conditions.

Engineering Practice and Wear Mechanism Analysis

Wear Mechanism Identification

The literature identifies three dominant wear mechanisms in the tested alloys:

1. Abrasive cutting: Hard carbide particles resist penetration by abrasive particles, creating micro-grooves rather than deep material removal. This mechanism dominates in two-body sliding against SiC.
2. Ploughing and matrix erosion: The ductile matrix undergoes plastic deformation around hard carbides, leading to material displacement rather than removal. This mechanism is prominent in slurry abrasion.
3. Fatigue spalling: Cyclic stress causes microcracks at carbide-matrix interfaces, leading to localized material detachment. This mechanism becomes significant in impact-abrasive conditions.

The optimal alloy design minimizes all three mechanisms simultaneously, which requires a balance of hard carbide particles (to resist cutting), tough matrix (to resist fatigue), and fine microstructure (to reduce crack initiation sites).

Process Parameters Affecting In-situ Carbide Formation