Low-Temperature Titanium Oxygen Hardening Without Distortion
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Solution Overview
Problem
Existing methods for hardening titanium and other Group IV metals often require high temperatures, leading to grain growth and distortion, and there is a need for a process that maintains the metallic appearance while achieving increased hardness.
Innovation Solution
A two-step process involving oxidation at low temperatures (up to 800°C) using CO2, N2O, or combinations to form a non-stratified oxide layer, followed by diffusion in an inert atmosphere to integrate oxygen into the metal, resulting in a superficial diffusion zone with enhanced hardness without altering the metal's appearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high temperature hardening is used to increase surface hardness, then hardness is improved, but grain growth and distortion occur
Solution Approach 1:
The invention changes the temperature parameter from conventional high temperature (900-1100°C) to low temperature (400-800°C) hardening process. This parameter change allows achieving the desired surface hardness (HV 600-1200) while preventing grain growth and dimensional distortion, as the lower temperature does not provide sufficient thermal energy for grain boundary migration and distortion
2Strength
If high temperature hardening is used to increase surface hardness, then hardness is improved, but metallic appearance is lost due to oxidation and colour changes
Solution Approach 1:
The invention changes the temperature parameter to below the oxidation threshold of titanium (800°C), preventing the formation of coloured oxide layers that would destroy the metallic appearance. The low temperature process maintains the silver-grey metallic lustre while still achieving the required surface hardness through controlled oxygen diffusion
Solution Approach 2:
The invention employs an inert or controlled atmosphere (vacuum, inert gas, or controlled oxygen potential) during the hardening process to prevent excessive oxidation and colour changes on the titanium surface. This atmospheric control allows the metal to maintain its characteristic metallic appearance while still absorbing sufficient oxygen for hardening
3Strength
If oxygen content is increased to improve hardness, then hardness is improved, but excessive oxidation occurs at high temperatures
Solution Approach 1:
The invention changes the temperature parameter to low temperature (400-800°C) where oxygen diffusion into titanium occurs at a controlled rate, allowing sufficient oxygen content (0.1-2.0 wt%) to be achieved for hardening without the excessive oxidation that occurs at high temperatures. The lower thermal energy provides better control over oxygen uptake
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 achieves a surface hardness increase of at least 200 HV0.025 units, maintaining the metallic lustre and original dimensions of the metal, with a diffusion zone containing interstitial oxygen, carbon, or nitrogen, suitable for applications requiring high hardness and aesthetics.
Implementation Method 1
oxidising the Group IV metal over an oxidising duration of at least 10 minutes in an oxidising atmosphere at a first temperature to provide a non-stratified Group IV metal oxide on the surface of the workpiece using a gaseous oxidising species selected from CO2, N2O and combinations of CO2 and N2O
Implementation Method 2
diffusing oxygen from the non-stratified Group IV metal oxide into the Group IV metal in an inert atmosphere at a second temperature in the range of 500° C. to 800° C. and at a partial pressure of the gaseous oxidising species of up to 10−4 mbar over a diffusive duration of at least 0.1 hour to provide a superficial diffusion zone comprising oxygen in solid solution
Data Source
AI summary
The present invention relates to a method of oxygen hardening a Group IV metal, the method comprising the steps of: providing a workpiece of a Group IV metal in its final shape; oxidising the Group IV metal over an oxidising duration of at least 10 minutes in an oxidising atmosphere at a first temperature to provide a non-stratified Group IV metal oxide on the surface of the workpiece using a gaseous oxidising species having an upper temperature limit of up to 800° C. wherein the first temperature is in the range of 500° C. and the upper temperature limit of the gaseous oxidising species; diffusing oxygen from the non-stratified Group IV metal oxide into the Group IV metal in an inert atmosphere at a second temperature in the range of 500° C. to 800° C. and at a partial pressure of the gaseous oxidising species of up to 10-4 mbar over a diffusive duration of at least 0.1 hour to provide a superficial diffusion zone comprising oxygen in solid solution. In another aspect, the invention relates to a Group IV metal component comprising a material core having a core hardness and a surface hardness of at least the core hardness +200 HV0.025. The component is obtainable in the method of the invention.