Thermal treatment method capable of effectively improving toughness and reducing anisotropy of LAM TC4

Abstract

The invention discloses a thermal treatment method capable of effectively improving toughness and reducing anisotropy of LAM TC4. In the laser additive manufacturing process, the layer-by-layer accumulation principle is adopted, quick heating and cooling are conducted, thus, a thick beta columnar crystal in an epitaxial growth form is likely to form, generally, the crystal is internally provided with alpha' martensite and an alpha widmanstatten structure, accordingly, the mechanical property of the LAM TC4 has obvious anisotropy, and the ductility and toughness are poor. Thus, the repeated cyclic thermal treatment and solid and aging thermal treatment method is adopted, the as-deposited structure of the LAM TC4 is converted into a duplex microstructure composed of coarsening equiaxial primary alpha phases, primary alpha strips and secondary precipitation alpha phases in a conversion beta substrate, wherein the primary alpha strips and the secondary precipitation alpha phases crisscrossand are distributed in a mesh basket shape. The anisotropy is reduced, the strength is ensured, and meanwhile, the plasticity and toughness of the alloy are effectively improved. The comprehensive mechanical properties of the LAM TC4 in the thermal treatment state are better than those of a forged piece of the same material, wherein the strength anisotropy is smaller than or equal to 4%, and thefracture toughness anisotropy is smaller than or equal to 9%.

Description

technical field [0001] The present invention relates to the application of LAM titanium alloy in aerospace, biological navigation, vehicle high-speed rail and other manufacturing fields, and in particular to the industrial manufacturing application field that has corresponding requirements for reducing the anisotropy of LAM TC4 titanium alloy and improving strength and toughness. Background technique [0002] Due to its excellent corrosion resistance, high specific strength and yield strength, TC4 titanium alloy is currently widely used in aerospace, navigation and biomedical industries. The use of laser additive manufacturing of TC4 alloy components has the advantages of low cost, short cycle time and high performance. However, due to the characteristics of rapid heating and cooling in the LAM process, the deposited structure of LAM TC4 alloy is quite different from that of traditional TC4 alloy casting and forging in terms of size, shape and distribution. Traditional TC4 ...

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Problems solved by technology

The as-deposited microstructure of LAM TC4 alloy is mainly composed of coarse β columnar grains running through the entire cladding layer and primary α laths at the grain boundaries. Acicular α′ martensite, α Widmanstatten structure, etc. lead to high strength, but poor plasticity and toughness, and the anisotropy of mechanical properties is relatively obvious. It is necessary to change the structure of LAM TC4 alloy parts by heat treatment. At present, it is an effective means to improve the mechanical properties of LAM TC4 alloy. However, the heating temperature of the existing heat treatment methods that can eliminate anisotropy and improve toughness is relatively close to or even exceed the β transformation temperature, resulting in serious coarsening of the alloy structure. With small anisotropy and increased toughness, the strength decreases greatly

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