TiAl Alloy Casting Mold with Weakening Layer
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Solution Overview
Problem
TiAl alloy cast products are prone to fractures or cracks due to differential thermal expansion between the alloy and the casting mold, causing tensile stress during the cooling process.
Innovation Solution
A casting mold with a reaction-resistant layer and a weakening layer formed from refractory materials, including cerium oxide and fused silica, is used to reduce the mold's strength and allow for controlled cracking, thereby releasing the TiAl alloy cast product and preventing fractures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional casting mold is used to cast TiAl alloy, then the mold maintains its shape and structural integrity, but the TiAl alloy cast product is likely to cause fractures or cracks due to tensile stress from differential thermal expansion during cooling
Solution Approach 1:
The casting mold is divided into multiple layers with different functions: a reaction-resistant layer (5μm to 2mm thickness) containing cerium oxide, yttrium oxide, and zirconium oxide to prevent chemical reactions with molten TiAl alloy, and a back-up layer (2mm to 50mm thickness) containing a weakening layer (80% to 100% silica material with 26% to 34% cristobalite) and a shape-retention layer to provide structural support. This segmentation allows the mold to have both controlled weakness for stress relief and sufficient shape retention capability.
Solution Approach 2:
The weakening layer is designed with specific material composition (80% to 100% silica material containing 26% to 34% cristobalite) and controlled thickness to reduce the overall strength of the casting mold. This parameter change enables the mold to develop controlled cracks during cooling, releasing tensile stress and preventing fractures in the TiAl alloy cast product while maintaining sufficient strength for shape retention.
2Reliability
If the casting mold strength is reduced to allow controlled cracking, then fractures in TiAl alloy cast product are suppressed, but the mold may lose its shape retention capability
Solution Approach 1:
The back-up layer is segmented into a weakening layer and a shape-retention layer. The weakening layer (80% to 100% silica material) is positioned to allow controlled cracking and stress relief, while the shape-retention layer provides the necessary structural support to maintain the mold's overall shape during the casting and cooling process.
Solution Approach 2:
The casting mold uses composite material structure combining different refractory materials with specific properties. The weakening layer uses silica material with controlled cristobalite content for stress relief, while the shape-retention layer uses refractory materials with higher strength characteristics. This composite structure enables simultaneous achievement of controlled weakness and shape retention.
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 solution effectively suppresses fractures and cracks in TiAl alloy cast products by allowing controlled cracking in the mold, ensuring the product is released without damage.
Implementation Method 1
a TiAl alloy cast product may cause fractures or cracks due to its shrinkage in a cooling process (from 1100° C. to 1000° C.) after the casting. To be more precise, at the time of cooling after the casting, the casting mold restrains the TiAl alloy cast product and applies a tensile stress to the TiAl alloy cast product because an amount of shrinkage of the TiAl alloy cast product becomes larger than an amount of shrinkage of the casting mold due to a difference in thermal expansion between the TiAl alloy cast product and the casting mold.
Data Source
AI summary
A casting mold to cast a TiAl alloy includes a casting mold body formed into a bottomed shape and provided with a cavity. The casting mold body includes a reaction-resistant layer provided on the cavity side, formed from a refractory material containing at least one of cerium oxide, yttrium oxide, and zirconium oxide and a back-up layer formed on the reaction-resistant layer. The back-up layer includes a weakening layer formed from a refractory material including a silica material in a range from 80% by mass to 100% by mass inclusive, the silica material containing cristobalite in a range from 26% by mass to 34% by mass inclusive and the rest being fused silica, the weakening layer being designed to reduce casting mold strength and a shape-retention layer formed from a refractory material.