Abrasive wear properties of stellite hardfacing alloys

Comparative study: MMA, TIG, and laser cladding

H. K. D. H. Bhadeshia

This study guide examines research regarding Stellite 6 cobalt-based alloys. It focuses on the relationship between deposition techniques, microstructural evolution, and abrasion resistance.

Part 1: Short answer quiz

Instructions: Formulate your answer in 2–3 sentences, then click "Check Answer" to compare with the study results.

1. How do the nominal heat inputs of MMA, TIG, and laser cladding compare, and what is the effect on microstructure?
The nominal heat inputs are 920 J/mm⁻¹ for MMA, 660 J/mm⁻¹ for TIG, and 240 J/mm⁻¹ for laser cladding. As heat input decreases, freezing rates increase, leading to a finer microstructural scale and higher hardness.
2. What is the relationship between deposition method and the degree of dilution?
The degree of dilution—the mixing of the substrate into the hardfacing layer—decreases in the order of MMA, TIG, and laser cladding. Lower dilution in laser cladding helps maintain the alloy's intended chemical composition and hardness.
3. Why did MMA samples exhibit the poorest wear resistance with Al₂O₃?
MMA samples possessed a coarser microstructure and lower starting hardness. They also exhibited an inadequate degree of strain hardening during the test, leading to constant and high wear rates.
4. Explain the significance of the fcc to hcp phase transformation.
This transformation acts as a strain-hardening mechanism. The hcp platelets formed during the process offer formidable obstacles to dislocation motion, increasing the material's resistance to further deformation.
5. How does iron content in TIG samples influence metallurgical stability?
High matrix iron content results in a higher stacking fault energy. This makes the matrix more stable against the fcc to hcp transformation, leading to lower densities of intrinsic stacking faults.

Part 2: Essay prepartion

Instructions: Use these prompts to outline your comprehensive responses. Click to reveal key talking points and evidence from the study.

Essay Topic: Mechanisms of Strain Hardening

Compare the behaviors of TIG and laser clad deposits regarding superior hardening.

Key Points:
  • Laser cladding allows for lower matrix stacking fault energy (SFE).
  • Low SFE facilitates rapid formation of hcp platelets from the fcc matrix.
  • TIG's higher iron dilution increases SFE, hindering this beneficial transformation.
Essay Topic: Impact of Abrasive Characteristics

Analyze how Al₂O₃ vs. SiC changes experimental outcomes.

Key Points:
  • Al₂O₃ (Alumina) reveals subtle differences in microstructural resistance.
  • SiC (~2480-2600 HV) is aggressive enough to wipe out microstructural advantages.
  • Wear rates become similar across all methods when the abrasive hardness significantly exceeds the alloy hardness.

Part 3: Glossary

Abrasive Wear
Material removal due to hard particles sliding against a surface.
Dilution
Change in deposit composition caused by mixing with the base metal.
fcc / hcp
Face-centered cubic (stable matrix) and hexagonal close-packed (wear-resistant phase).
Laser Cladding
Low-heat input process resulting in high cooling rates and low dilution.
Vickers Hardness (HV)
Standard measure of hardness based on resistance to diamond indentation.