Sintered Titanium Aluminide Articles via Pre-Alloyed Aluminum
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Solution Overview
Problem
The high melting point difference between titanium and aluminum, along with processing issues, complicates the preparation of gamma titanium aluminide (γ-TiAl) compositions for automotive applications, leading to limited use due to high porosity and slow sintering processes in existing methods.
Innovation Solution
A method involving the use of substantially pure titanium particles sintered with rapidly solidified aluminum particles containing minor alloying elements like Nb, Cr, Mn, Mo, Si, Cu, Fe, Sn, and V, where the aluminum is pre-alloyed with these elements to form a homogeneous liquid, which is then rapidly cooled and mixed with titanium, promoting rapid inter-diffusion and reducing porosity during the sintering process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If blended elemental powder mixtures of titanium and aluminum are used for sintering, then the desired γ-TiAl composition can be achieved, but the sintering process is slow and produces high porosity due to the nearly one thousand degree Celsius difference in melting points
Solution Approach 1:
The invention applies preliminary action by pre-alloying aluminum with minor alloying elements (Nb, Cr, Mn, Mo, Si, Cu, Fe, Sn, V) before sintering. This pre-mixing and pre-alloying step ensures homogeneous distribution of alloying elements in the aluminum matrix, which then facilitates uniform inter-diffusion with titanium particles during sintering, achieving desired microstructure quality without requiring excessively long sintering times.
Solution Approach 2:
The invention changes the physical state parameter of aluminum from solid to liquid during sintering by utilizing its lower melting point. The process is conducted at temperatures between the melting point of aluminum (660°C) and the melting point of titanium (1668°C), creating a liquid aluminum phase that dramatically accelerates inter-diffusion with solid titanium particles, thereby increasing sintering speed while maintaining microstructure quality.
2Manufacturing precision
If blended elemental powder mixtures are used, then γ-TiAl composition can be formed, but porosity is high due to slow inter-diffusion caused by melting point differences
Solution Approach 1:
The invention changes the phase state of aluminum to liquid during sintering by controlling temperature between the melting points of aluminum and titanium. This liquid phase enables rapid atomic diffusion and eliminates porosity by allowing complete inter-diffusion between aluminum and titanium particles, producing dense, high-quality γ-TiAl microstructure with minimal voids or defects.
Solution Approach 2:
The invention creates a composite powder mixture consisting of pre-alloyed aluminum particles containing dissolved alloying elements combined with titanium particles. This composite approach ensures that alloying elements are uniformly distributed within the aluminum phase before contact with titanium, leading to homogeneous γ-TiAl formation with consistent properties throughout the sintered product.
3Reliability
If individual elemental additions of alloying elements are made to titanium and aluminum separately, then selective enhancement of ductility and corrosion resistance is achieved, but processing becomes complicated due to widely-varying melting points of elements
Solution Approach 1:
The invention merges multiple alloying elements (Nb, Cr, Mn, Mo, Si, Cu, Fe, Sn, V) into a single aluminum-based pre-alloy. By dissolving all these elements with widely-varying melting points into liquid aluminum before solidification, the process simplifies manufacturing by eliminating the need to handle and process each element separately, while still achieving selective enhancement of material properties through controlled composition.
Solution Approach 2:
The invention uses aluminum as an intermediary carrier for alloying elements. Instead of adding elements directly to titanium or handling them as separate powders, the alloying elements are first incorporated into aluminum (which has a lower melting point and good solubility for many elements), creating a pre-alloy that then reacts with titanium during sintering. This intermediary approach simplifies processing while maintaining property enhancement.
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
This approach results in a more rapid sintering process with reduced porosity, achieving the desired microstructure of γ-TiAl with minor alloying additions, enhancing the properties of titanium alloy articles for automotive components.
Implementation Method 1
The liquid is then rapidly solidified by a suitable practice to obtain flakes or other particle shapes
Implementation Method 2
The X elements are initially carried or transported in aluminum, preferably liquid aluminum, for inter-diffusion with titanium particles during the sintering process
Implementation Method 3
This invention pertains to methods of sintering compacted preform mixtures of substantially pure titanium particles with particles of rapidly solidified mixtures of aluminum and the other alloying element(s) to form such articles with low porosity and desired microstructures
Data Source
AI summary
A process for fabricating sintered, substantially pore-free titanium aluminide articles with minor alloying element additions is disclosed. Such articles may find application as automobile engine valves and connecting rods and may be fabricated by rapidly sintering intimately mixed powders of substantially pure titanium and rapidly-cooled particles of aluminum alloyed with the minor alloying element(s).