Cladding-Spraying Composite Process for Strengthening Wear Parts Study Note

Literature Overview

This 1991 publication by Luo Wenling, Ren Shencheng, and Ji Hanxiong from the Heilongjiang Institute of Mechanical Engineering Research, published in the journal "Construction Mechanization," presents a novel approach to surface strengthening of wear-critical components through the combination of weld cladding and thermal spraying. The composite process leverages the deep, metallurgically bonded overlay of cladding with the rapid quenching and fine microstructure of thermal spraying, creating a synergistic surface layer that outperforms either process used alone.

Technical Rationale for Composite Approach

The fundamental insight driving this research is that no single surface engineering process can simultaneously optimize all performance parameters. Weld cladding provides excellent metallurgical bonding and thick deposits but produces relatively coarse microstructures. Thermal spraying produces fine, rapidly solidified microstructures with high hardness but has limited deposit thickness and concerns about inter-splat bonding quality.

Process Comparison: Cladding vs. Spraying vs. Composite

The composite approach exploits the complementary strengths: the cladding layer provides bulk thickness, metallurgical bonding, and a thermally stable foundation, while the sprayed layer provides the ultra-fine microstructure, high hardness, and compressive residual stresses that enhance fatigue and wear resistance.

Process Development and Parameters

Typical Composite Process Sequence

1. Base preparation — Grind wear surface to Ra 12.5 μm, remove contaminants.
2. Preheating — Heat base to 200–300°C (depending on base material and overlay alloy).
3. Cladding pass 1 — Apply 2–3 mm overlay using SAW or GMAW.
4. Interpass grinding — Light grind to remove surface oxide and defects.
5. Cladding pass 2 — Apply additional 1–2 mm if required.
6. Surface preparation for spraying — Sandblast to Sa 2.5, Ra 25–50 μm.
7. Thermal spraying — Apply 0.5–2.0 mm spray coating using HVOF or plasma spraying.
8. Post-treatment — Optional stress relief at 350–400°C for 1–2 hours.

Cladding Layer Parameters

Spraying Layer Parameters

Microstructural Analysis

The composite layer microstructure exhibits a gradient character:

1. Spray layer (surface) — Rapidly solidified dendritic structure with retained metastable phases, carbide particles with fine morphology, compressive residual stresses of 200–500 MPa.
2. Cladding layer (subsurface) — Coarser grain structure with equilibrium phases, martensitic or austenitic matrix with carbide precipitates, tensile residual stresses partially offset by spray layer.
3. Interface zone — Transition region where thermal effects from spraying have slightly modified the cladding microstructure (tempering effect if spray temperature is sufficient).

The key microstructural benefit is the compressive residual stress field introduced by the thermal spray process. This compressive stress counteracts the tensile residual stresses from the cladding process and provides significant improvement in fatigue resistance and resistance to spalling under impact loading.

Application to Construction Equipment Wear Parts

The research specifically targeted wear parts used in construction and earthmoving equipment, where the wear conditions are characterized by:

• High-impact loading (excavator buckets, bulldozer blades)
• Abrasive sliding against soil and rock (grader blades, scraper bowls)
• Adhesive wear from metal-to-metal contact (hydraulic cylinder rods)
• Corrosive attack from moisture and chemicals (dump truck beds)

Performance Results

The life improvement factor of 4–6× over the base material, and 1.5–2× over cladding alone, demonstrates the clear benefit of the composite approach. The economic analysis shows that despite the higher processing cost of the composite process, the cost per hour of service life is 60–70% lower than using cladding alone.

Quality Control and Defect Analysis

Critical Quality Attributes

Common Defects in Composite Process