Zhuojin Pipe Fitting Co., LtdComposite Overlay Welding and Thermal Spray Process for Strengthening Wear-Prone Components
Literature Overview
The 1991 paper by Luo Wenling, Ren Shencheng, and Ji Hanxiong from the Heilongjiang Institute of Mechanical Industry Research, published in "Construction Mechanization," investigates the combined application of overlay welding and thermal spray (thermal dissolution) surface technologies for strengthening wear-prone components. The abstract explicitly states that neither technology alone produces optimal results for certain applications, motivating the development of a composite approach. The classification TG455 confirms the surface engineering focus, while the keywords—overlay welding, thermal spray, brick-making machine, spiral auger—indicate the specific industrial application.
Rationale for Composite Surface Engineering
The paper's central thesis is that the combination of overlay welding and thermal spray can achieve synergistic improvements in wear resistance that neither technology alone can provide. This insight is based on the understanding that different surface technologies offer complementary benefits:
| Technology | Primary Benefit | Limitation |
|---|---|---|
| Overlay welding | Deep bond strength, thick deposits, good toughness | Surface hardness limited by dilution, residual stress |
| Thermal spray | High surface hardness, low dilution, fine microstructure | Thin deposits, limited bond strength, poor impact resistance |
| Composite approach | Combines deep toughness with hard surface | Process complexity, interface quality control |
The spiral auger of a brick-making machine is an excellent example of a component where this composite approach is advantageous. The auger experiences:
- Severe abrasive wear from clay and soil particles
- Impact loading from material bridging and chunking
- Corrosive attack from moist clay containing organic matter
- Thermal cycling from frictional heating
No single surface technology adequately addresses all these degradation mechanisms simultaneously.
Process Development
Composite Process Sequence
The composite process involves the following steps:
- Base component preparation: Machining or grinding of the wear surface to remove defects and provide a sound substrate
- Overlay welding: Application of a thick (2–5 mm) overlay layer using SMAW or FCAW with a tough, high-toughness alloy (e.g., high-Cr martensitic or austenitic)
- Post-weld machining: Grinding or machining the overlay to a smooth surface suitable for thermal spraying
- Thermal spray: Application of a thin (0.5–2 mm) hard surface layer using flame spray, plasma spray, or HVOF
- Post-spray treatment: Optional heat treatment to relieve residual stress and optimize microstructure
Material Selection for the Composite System
| Layer | Material | Function | Typical Properties |
|---|---|---|---|
| Base | Q235 or 45 steel | Structural support | HB 120–180 |
| Overlay weld | Cr15–Cr25 martensitic | Toughness, corrosion resistance | HRC 50–58, CVN > 27 J |
| Thermal spray | WC-Co, CrC-NiCr, or TiC-NiCr | Surface hardness, wear resistance | HRC 65–80 |
The overlay welding layer provides the necessary toughness to resist impact loading and the corrosion resistance to withstand the moist clay environment. The thermal spray layer provides the extreme surface hardness required to resist abrasive wear. The interface between the two layers is critical—poor bonding can lead to delamination under cyclic loading.
Interface Quality Control
The quality of the interface between the overlay weld and the thermal spray layer is determined by:
| Factor | Requirement | Verification Method |
|---|---|---|
| Surface cleanliness | Free of oxide, grease, dust | Visual inspection, solvent cleaning |
| Surface roughness | Ra 3.2–6.3 μm | Roughness tester |
| Preheat temperature | 150–250 °C | Thermocouple measurement |
| Spray angle | 80–90° to surface | Visual or mechanical guide |
| Bond strength | > 20 MPa (ASTM C236) | Adhesion test |
Application to Spiral Auger Components
The spiral auger of a brick-making machine is a rotating component with a helical flight that transports clay from the hopper to the forming die. The flight experiences:
- Abrasive wear: From clay particles containing quartz and other hard minerals
- Impact wear: From material bridging and the sudden release of stuck material
- Corrosive wear: From moist clay with organic acids and sulfates
- Fatigue: From cyclic bending during rotation
The composite surface engineering approach addresses these mechanisms as follows:
| Degradation Mechanism | Mitigation by Composite Process |
|---|---|
| Abrasive wear | Hard thermal spray surface (HRC 65–80) resists particle indentation |
| Impact wear | Tough overlay weld layer absorbs impact energy |
| Corrosive wear | High-Cr overlay layer provides passive film resistance |
| Fatigue | Overlay weld layer provides fatigue-resistant microstructure |
Performance Evaluation
The paper likely presents comparative wear test results demonstrating the superiority of the composite approach. Typical results for such applications include:
| Treatment | Wear Life Relative to Base | Surface Hardness |
|---|---|---|
| Uncoated base steel | 1× (reference) | HB 150–180 |
| Overlay welding only | 3–5× | HRC 50–58 |
| Thermal spray only | 4–6× | HRC 65–75 |
| Composite process | 8–12× | HRC 65–80 (surface) |
These improvements are achieved while maintaining the structural integrity of the base component, which is critical for safety-critical rotating machinery.
Study Insights and Reflections
This paper represents an early but important recognition of the principle of multi-layer surface engineering. The insight that combining technologies can produce synergistic effects is now well-established in the field of surface engineering, but it was relatively novel in the early 1990s Chinese industrial context. The paper's focus on practical industrial application—brick-making machinery—rather than laboratory research reflects the applied orientation of the authors' institution.
The key technical challenge in composite surface engineering is the interface between layers. Each additional interface introduces a potential failure path. The paper's implicit emphasis on surface preparation and process parameter control for each layer reflects an understanding that the composite process is only as strong as its weakest interface.
From a modern perspective, this work anticipated the development of more sophisticated multi-layer surface engineering approaches, including functionally graded coatings, laser cladding combined with thermal spray, and multi-pass laser melting. The fundamental principle—combining technologies to achieve complementary performance—remains valid and is actively pursued in current research and industrial practice.
The paper also highlights the importance of matching the surface engineering solution to the specific service conditions. The brick-making machine auger is a demanding but not extreme application, making it an ideal candidate for cost-effective composite surface engineering. More severe applications might require more advanced technologies, but the principles of layer design and interface management remain the same.