Thermal Spray Adhesion via Surface Undercuts

Solution Overview

Problem

Conventional thermal spraying processes face challenges in achieving strong adhesion of thermally sprayed layers on metallic substrates due to high temperature differences and mechanical stresses, leading to detachment under alternating thermal and mechanical loads.

Innovation Solution

A multistage surface treatment process involving initial material removal to create raised microstructures followed by a second step that forms undercuts through shaping or breaking, allowing for enhanced mechanical clamping and improved adhesion by allowing the thermal spray layer to infiltrate and contract without detaching from the substrate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If thermal spray layers are deposited onto metallic substrates, then coating is achieved, but high temperature differences cause high mechanical tensions that adversely affect layer adhesion

Engineering Contradiction:

Improvelayer adhesionVSAvoidmechanical tensions

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The substrate surface is pre-conditioned with roughened structures and undercuts before thermal spray deposition. This preliminary surface preparation creates mechanical interlocking features that compensate for the thermal stress generated during spraying, allowing the layer to adhere better despite the temperature differences.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The surface topology is modified by changing the physical parameters of the substrate surface, specifically by creating roughened structures with undercuts. This parameter change in surface geometry provides mechanical anchoring that counteracts the adverse mechanical tensions from thermal expansion differences.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If conventional roughening processes are used, then surface area is increased, but adhesive strength is insufficient under alternating thermal loads and mechanical stresses

Engineering Contradiction:

Improveadhesive strengthVSAvoiddetachment under thermal and mechanical loads

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The substrate surface is pre-conditioned with roughened structures and undercuts before thermal spray deposition. This preliminary surface preparation creates mechanical interlocking features that compensate for the thermal stress generated during spraying, allowing the layer to adhere better despite the temperature differences.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The surface topology is modified by changing the physical parameters of the substrate surface, specifically by creating roughened structures with undercuts. This parameter change in surface geometry provides mechanical anchoring that counteracts the adverse mechanical tensions from thermal expansion differences.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If material removal is increased to create better surface structures, then adhesion improves, but material loss and process complexity increase

Engineering Contradiction:

ImproveadhesionVSAvoidmaterial removal

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

Instead of removing large amounts of material, the process applies partial action by creating surface roughness and undercuts through controlled material displacement rather than extensive removal. The second step forms undercuts by shaping existing raised structures with minimal additional material removal, achieving adequate adhesion with limited material loss.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The process replaces aggressive mechanical material removal with a more refined approach using controlled plastic deformation and localized shaping in the second step. This substitution reduces material loss while still creating the necessary undercut structures for adhesion.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The process significantly increases the adhesive strength of thermal spray layers by creating undercuts that prevent contraction and enhance mechanical clamping, even with low material removal in the second step, resulting in improved surface adhesion and wear protection.

Implementation Method 1

In the conventional thermal spraying processes such as plasma spraying, flame spraying, high-speed flame spraying or arc wire spraying, the spray particles are deposited onto the cold substrate in the molten state

Methodology Applied

Scientific EffectThermal spraying: Plasma Spray

Implementation Method 2

the spray particles are deposited onto the cold substrate in the molten state and quenched at a high cooling rate

Methodology Applied

Scientific EffectQuenching: Freezing

Data Source

PatentUS8209831B2Surface conditioning for thermal spray layers

Publication Date: 2012.07.03 MERCEDES BENZ GROUP AG

AI summary

The invention relates to a process for roughening metal surfaces to improve adhesion of layers which are thermally sprayed thereon, in that in a first process step recesses or depressions (2) are introduced into the surface in a material-detaching or material-removing treatment so that the protruding metal of the surface forms raised microstructures (3), in particular projections, ridges, protuberances or bumps, these microstructures being reworked in at least a second process step by shaping and/or breaking so that a significant proportion of the structures form undercuts (4) in relation to the surface.