Mechanical Properties of PTA Arc Cladding Alloys

Literature Overview

Published in 2007 by Liu Zhengjun, Liu Changjun, Wan Qian, and Yin Yijun from Shenyang University of Technology and Shenyang Blower and Fan Co., Ltd., this study investigates the mechanical properties of plasma transferred arc (PTA) cladding alloys. Supported by the Liaoning Provincial Natural Science Foundation (Grant No. 200412025), the research addresses the fundamental relationship between PTA processing parameters, microstructure, and the resulting mechanical behavior of overlay deposits.

Core Technical Objectives

The study aimed to systematically characterize the mechanical properties of PTA cladding layers, including hardness, tensile strength, impact toughness, and creep resistance, across different alloy systems and processing conditions. The industrial context was the demand for wear-resistant and corrosion-resistant overlays in blower and fan components exposed to abrasive and corrosive gas streams.

Microstructural Characteristics

PTA cladding deposits exhibit distinctive microstructural features that directly influence mechanical performance:

Hardness Distribution Analysis

The hardness profile through the cladding thickness follows a characteristic pattern: the bond line region typically exhibits lower hardness (200–350 HV) due to dilution with the base metal, while the upper layers achieve peak hardness (400–650 HV depending on alloy composition). The hardness gradient is governed by the dilution ratio at each pass, with the first pass experiencing the highest dilution and subsequent passes approaching the powder composition.

Typical hardness values for common PTA overlay alloys include:

Mechanical Property Results

Tensile and Fracture Behavior

Tensile testing of PTA overlay specimens revealed that the fracture location is strongly dependent on the dilution ratio and the number of passes. Specimens with dilution below 10% typically fracture within the overlay layer itself, indicating that the bond interface is stronger than the overlay. When dilution exceeds 20%, fractures shift to the bond line or base metal HAZ, indicating a weakened interface.

The tensile strength of the overlay layer generally ranges from 450–750 MPa for Ni-based alloys and 600–900 MPa for Co-based alloys. However, elongation values are typically low (3–8%), reflecting the inherently brittle nature of many hardfacing and wear-resistant overlay alloys.

Creep and High-Temperature Performance

For applications in hot gas environments (blowers, turbines, valves), creep resistance is critical. The study found that PTA deposits with refined microstructure (achieved through lower heat input and higher travel speed) exhibited superior creep resistance compared to deposits with coarsened grain structures. The creep life at 650°C under 100 MPa stress was improved by 40–60% when the grain size was refined from 50 μm to 15 μm through processing parameter optimization.

Process Parameter Effects on Mechanical Properties

The study systematically varied key PTA parameters and recorded their effects:

Optimal Processing Window

The study identified an optimal processing window for achieving a balance between hardness and toughness:

• Arc current: 120–160 A
• Travel speed: 350–500 mm/min
• Powder feed rate: 0.5–0.7 kg/min
• Shielding gas: 25–35 L/min Ar
• Interpass temperature: 80–120°C
• Number of passes: 3–5 for full thickness

Engineering Implications

The key engineering insight from this work is that mechanical properties of PTA cladding layers are not fixed material properties but are process-dependent variables. Two deposits produced from the same powder feedstock can exhibit hardness differences of 100–150 HV and toughness differences exceeding 50% depending on processing parameters. This has direct implications for quality control in production environments: process parameter documentation and in-process monitoring are essential for ensuring consistent overlay performance.

For blower and fan applications specifically, the selection of overlay alloy must balance wear resistance against the need for impact toughness, as these components may experience vibration and occasional impact loading. A Ni-based overlay with moderate hardness (300–350 HV) often outperforms a high-hardness Co-based overlay in terms of overall service life when the service environment includes both wear and thermal cycling.

Study Insights

This 2007 study contributed valuable quantitative data to the understanding of PTA overlay mechanical behavior. The systematic approach to correlating processing parameters with microstructure and properties represents a methodology that remains applicable in modern overlay engineering. The findings reinforce the principle that overlay design must be holistic—considering not just the surface layer properties but also the bond line integrity, HAZ characteristics, and residual stress state.