Titanium Alloy Case Hardening for Spallation Resistance
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Solution Overview
Problem
Existing methods for case hardening titanium alloys do not effectively achieve a thick, hard diffusion zone with improved mechanical properties, wear resistance, and corrosion resistance, often resulting in spallation and limited hardness due to the presence of hydrogen and impermeable surface layers.
Innovation Solution
A method involving a titanium alloy component treated in a reactive atmosphere with carbon and oxygen at elevated temperatures to form a diffusion zone with a carbo-oxide compound, ensuring a thickness of at least 50 μm and microhardness of 800 HV0.025, which is hydrogen-free and tightly integrated with the core, enhancing surface hardness and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional case hardening methods are used to increase surface hardness, then surface hardness is improved, but the hardened layer becomes prone to spallation and wear
Solution Approach 1:
The invention changes the chemical composition parameters of the hardened layer by strictly controlling oxygen content to 0.01-5 wt% and completely eliminating hydrogen. This parameter optimization creates a hardened layer with enhanced adhesion to the substrate, preventing spallation while achieving high surface hardness through controlled diffusion processes.
Solution Approach 2:
The invention creates a composite structure consisting of a hardened surface layer with specific oxycarbide composition (0.1-10 wt% oxygen, 0.1-5 wt% carbon) bonded to the titanium alloy substrate. This composite architecture combines the hardness benefits of oxide/carbide compounds with the ductility and adhesion of the metal substrate, preventing delamination.
2Strength
If hydrogen is added during case hardening to increase hardness, then surface hardness is improved, but embrittlement occurs
Solution Approach 1:
The invention extracts and completely removes hydrogen from the case hardening process and resulting hardened layer. By eliminating this harmful element while maintaining other alloying elements at controlled levels, the method achieves high surface hardness without the embrittlement that would otherwise result from hydrogen incorporation.
Solution Approach 2:
The invention optimizes the chemical composition parameters by setting hydrogen content to 0 wt% and carefully controlling oxygen and carbon content ranges. This parameter optimization prevents embrittlement while still achieving the desired hardness improvement through controlled diffusion of beneficial elements.
3Reliability
If diffusion zone thickness is increased to improve mechanical properties, then wear resistance is improved, but the treatment time and temperature requirements increase
Solution Approach 1:
The invention optimizes the diffusion process parameters including temperature range (800-1100°C), time duration (1-24 hours), and atmospheric composition to achieve an optimal diffusion zone thickness of 10-500 μm. These parameter optimizations enable sufficient wear resistance to be achieved in practical treatment times without requiring excessively high temperatures or prolonged exposure.
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 method produces a titanium alloy component with a hardened surface resistant to wear and spallation, achieving microhardness of 1200 HV0.025 and surface hardness of 1500 HV, while maintaining corrosion resistance and preventing embrittlement.
Implementation Method 1
a surface-adjacent diffusion zone in the titanium alloy, which provides the hardened titanium alloy with resistance to spallation, wear and corrosion as well as a hard surface
Implementation Method 2
the article is heat treated for a period of at least 12 hours at a temperature in the range of 850 to 900° C. at a pressure close to atmospheric pressure with a concentration of oxygen
Implementation Method 3
The pack carburisation is carried out with a limited amount of oxygen, at a temperature of 925° C. for 20 hours, which resulted in a multilayer structure comprising a titanium carbide (TiC) network layer atop of a relatively thick α-titanium oxygen diffusion zone
Data Source
AI summary
The present invention relates to a case hardened component of a titanium alloy, the component having a diffusion zone of a thickness of at least 50 μlτl, as calculated from the surface of the component, the diffusion zone comprising oxygen and carbon in solid solution and having a distinct phase of a carbo-oxide compound having the composition TiOxC1-x, wherein x is a number in the range of 0.01 to 0.99, which diffusion zone has a microhardness of at least 800 HV0.025 and which carbo-oxide compound has a microhardness of at least 1200 HV0.025. In another aspect the invention relates to a method of producing the case hardened component. In a further aspect the invention relates to a method of oxidising a component of a Group IV metal.