Beta-C Titanium Alloy Composition for Threaded Fatigue Strength
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Solution Overview
Problem
Current titanium alloy fasteners, particularly those made from Ti-6Al-4V and beta titanium alloys like Beta-C, face limitations in diameter size and mechanical properties such as ultimate tensile strength, double shear strength, and threaded fatigue strength, due to intergranular fatigue failure and grain boundary alpha phase issues.
Innovation Solution
A meta-stable β titanium alloy with a carbon content exceeding 0.05 wt.%, up to 0.25 wt.%, is developed to enhance mechanical properties. This alloy, within the composition range of standard Beta-C, includes intentional addition of carbon to refine alpha precipitation, reduce grain boundary alpha phase, and improve heat treatability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If beta titanium alloys are used to achieve higher strength, then ultimate tensile strength and double shear strength are improved, but intergranular fatigue failure occurs due to grain boundary alpha phase
Solution Approach 1:
The invention changes the chemical composition parameters by adding carbon (0.05-0.25 wt.%) to the beta titanium alloy, which fundamentally alters the phase transformation behavior during heat treatment. This parameter change enables the formation of a refined microstructure with eliminated grain boundary alpha phase while maintaining high strength, thereby resolving the contradiction between strength and fatigue resistance
Solution Approach 2:
The invention utilizes controlled phase transitions during heat treatment processes (solution treatment followed by aging) to transform the microstructure. The carbon addition facilitates a specific phase transition sequence that produces fine alpha precipitates within beta grains while preventing grain boundary alpha formation, thus achieving both high strength and improved fatigue properties
2Strength
If standard Beta-C alloy composition is used, then high strength is achieved, but diameter size is limited to 25.4 mm due to mechanical property limitations
Solution Approach 1:
By modifying the carbon content parameter from the standard Beta-C specification (≤0.05 wt.%) to a higher range (0.05-0.25 wt.%), the invention fundamentally changes the alloy's hardenability and phase transformation characteristics. This enables the production of larger diameter fasteners with uniform microstructure and enhanced mechanical properties throughout the cross-section, removing the 25.4 mm diameter limitation
3Reliability
If carbon content is increased to refine alpha precipitation and eliminate grain boundary alpha phase, then threaded fatigue strength is improved, but excessive carbon may cause other issues
Solution Approach 1:
The invention precisely defines the carbon content range (0.05-0.25 wt.%) to optimize the balance between beneficial effects (alpha precipitation refinement, grain boundary alpha elimination) and potential adverse effects. This controlled parameter change ensures sufficient carbon for microstructure refinement while preventing excessive carbide formation that would harm ductility and fatigue properties, achieving stable composition with improved reliability
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 modified alloy achieves significant improvements in ultimate tensile strength, double shear strength, and threaded fatigue strength, while maintaining ductility and reducing the propensity for intergranular failure, thus offering enhanced performance for titanium alloy fasteners.
Implementation Method 1
accelerate and refine alpha precipitation
Implementation Method 2
heat treatable to attain enhanced physical properties
Data Source
AI summary
A “modified” meta-stable #titanium alloy that, apart from carbon content, corresponds to the composition range for standard Beta-C titanium alloy. The modified alloy comprises vanadium, chromium, molybdenum, zirconium, aluminium, with maxima for oxygen, iron, nitrogen, hydrogen, yttrium, and other elements (apart from carbon and titanium), with a balance (apart from carbon) of titanium. The modified alloy has carbon present at a stable total carbon level sufficiently in excess of 0.05 wt. % achieving an improvement in the mechanical properties of UTS, DSS and fatigue strength in threaded regions, relative to standard Beta-C alloy with a specified carbon level below 0.05 wt. %, with a maximum carbon content controlled so as to preclude carbide formation having a detrimental effect on the level of fatigue strength.