Development of Flexible Strip Surfacing Materials for Thin-Walled Component Application

Literature Overview

Published in Welding (2010, Issue 12, pp. 46-48), this paper by Song Dan, Li Deyuan, Liu Xiaoshu from Shenyang University of Technology, and Peng Yang from Shenyang Bolite Welding Materials Co., Ltd. addresses a significant gap in surfacing technology: the application of hardfacing materials to thin-walled components and internal surfaces where conventional electrodes cannot be effectively applied. The research was funded by the Liaoning Provincial Department of Education Science and Technology Fund.

Technical Challenge and Solution Concept

Conventional surfacing methods face fundamental limitations when applied to thin-walled tubing and internal surfaces:

Challenge	Conventional Limitation	Flexible Strip Solution
Thin wall distortion	High heat input causes warping	Low heat input from narrow strip
Internal surface access	Electrode cannot reach	Flexible strip conforms to geometry
Dilution control	High dilution with thick deposits	Thin, controlled deposit thickness
Multi-direction welding	Positional limitations	Strip can be pre-positioned
Heat-affected zone	Wide HAZ on thin sections	Narrow HAZ from TIG process

The flexible strip concept involves creating a pre-formed surfacing material in strip form that can be bent and shaped to conform to the substrate geometry before welding. This pre-forming capability enables application to complex geometries that are inaccessible to conventional consumables.

Material Development and Composition

The strip material combines Ni60 (a nickel-based austenitic alloy) with WC (tungsten carbide) powder particles, bonded together with organic silicone adhesive. The composition design addresses multiple requirements simultaneously:

Ni60 matrix: Provides excellent crack resistance, high temperature strength, and good bonding to most substrates
WC particles: Provide extreme hardness (HV 1500-2000) and abrasion resistance
Organic silicone adhesive: Provides flexibility during forming, burns off cleanly during welding, and does not contaminate the weld metal

Adhesive Selection Study

The authors systematically evaluated different adhesive materials for strip formation:

Adhesive Type	Forming Performance	Weld Quality	Cost	Recommendation
Organic silicone	Excellent flexibility	Clean burn-off, no contamination	Moderate	Preferred
Other adhesives	Variable	Potential contamination	Variable	Less suitable

The organic silicone adhesive was selected as optimal because it:

Maintains flexibility during forming and installation
Decomposes cleanly at welding temperatures without leaving residues
Does not react with the Ni60-WC material during welding
Provides sufficient bond strength during handling and positioning
Allows controlled thickness of the strip material

Manufacturing Process

The strip fabrication process involves several critical steps:

Material mixing: Ni60 powder and WC particles are uniformly blended with the adhesive binder
Forming: The mixture is formed into strip shape using molds or rolling
Drying/curing: The formed strips are dried to achieve handling strength
Storage: Proper storage conditions prevent premature curing or degradation
Application: Strips are bent to conform to substrate geometry and welded in place

Process Parameters for TIG Welding

Parameter	Typical Range	Notes
Welding method	TIG (GTAW)	Low heat input, clean weld
Current type	DCEN	Deep penetration, stable arc
Current range	80-150 A	Depends on strip thickness
Shielding gas	Argon	Prevents oxidation
Travel speed	Moderate	Controlled heat input
Preheating	Minimal or none	Low heat input requirement

Microstructural Analysis

Metallographic examination of the deposited layers revealed:

Matrix structure: Austenitic Ni60 matrix with retained austenite, providing toughness
Hard particles: WC particles dispersed throughout the matrix, providing wear resistance
Bond interface: Good metallurgical bonding between deposit and substrate
Porosity: Minimal porosity when proper TIG technique is applied

The Ni60-WC composite structure provides a favorable combination of properties:

High hardness from WC particles (target HV 800-1200 for the composite)
Good toughness from the austenitic Ni matrix
Excellent crack resistance from the austenitic structure
Good corrosion resistance from the nickel-rich matrix

Application Scenarios

The flexible strip material addresses specific industrial needs:

Application	Substrate	Service Condition	Advantage
Thin pipe internal lining	Carbon steel tubing	Abrasive slurry flow	Internal access, low distortion
Small diameter valve seats	Alloy steel	High pressure, wear	Conformal application
Hydraulic cylinder bores	Steel	Sliding wear	Internal surface coverage
Turbine blade tips	Superalloy	High temperature, erosion	Precise positioning
Small fitting repair	Various	Localized wear	Targeted application

Quality Control Considerations

For production implementation, the following quality control measures are essential:

Strip material quality: Uniform particle distribution, consistent thickness, proper cure state
Surface preparation: Clean, oxide-free substrate for proper bonding
Welding parameters: Documented and controlled for each application
Post-weld inspection: Visual examination, hardness verification, and possibly UT for bond quality
Performance testing: Wear testing under representative conditions

Study Insights and Engineering Reflection

This research addresses a genuine gap in surfacing technology. The limitation of conventional consumables for thin-walled and internal surface applications has long constrained engineers from applying hardfacing protection to components where it would be most beneficial. The flexible strip concept provides a practical solution that leverages existing TIG welding infrastructure while adding the versatility of pre-formed consumable geometry.

The choice of Ni60-WC as the base material system is well-considered: Ni60 provides the crack resistance and bonding capability that WC alone cannot offer, while WC provides the hardness that Ni60 alone cannot achieve. The composite approach follows the well-established principle that combining hard and tough phases in a composite structure achieves properties superior to either phase alone.

The adhesive technology, while seemingly simple, represents a critical enabling technology. The requirement for clean burn-off without contamination is demanding, and the selection of organic silicone represents a careful balance of forming capability and welding compatibility. Future development should explore alternative binder systems that may offer improved storage stability and handling characteristics.

This work demonstrates that creative adaptation of existing materials and processes can solve practical engineering problems that have resisted conventional approaches, offering engineers a new tool for component protection in challenging geometries.