Advantages and applications of medical titanium alloy in medical device manufacturing

When titanium rods and titanium alloy rods are heated to β phase, a → β polymorphic transformation occurs. Sometimes this process is also called recrystallization. The transition temperature of a→β of high purity titanium is 875+-5. But until the β phase is completely formed, it is difficult to observe this process with metallographic methods. The reason why phase β appears at low temperature is unclear. But the experiment pointed out that a and β mutually transform, whether it is heating or cooling, a phase and β phase always maintain a certain Bragg orientation relationship. There has been little research on the polymorphic transformation during heating in titanium alloys.

1. The transformation of titanium rods and titanium alloy rods during slow cooling

When titanium rods and titanium alloy rods are slowly cooled from the β phase region to the a + β phase region, a polymorphic transition of β → a will occur. It has been confirmed in high-purity titanium that the nucleation of phase a is martensitic at this time, and the growth depends on the thermal activation process. During the nucleation, the surface of the sample also has the bumps that occur during the martensitic transformation, and it also maintains a strict Bragg orientation relationship with the parent phase.

2. Transition in rapid cooling

The transformation of titanium rods and titanium alloy rods during rapid cooling from the β-phase region and the transformation products are different with the changes of the β-stabilizing element content. Martensitic transformation: 1.a`Block martensite cannot measure the orientation relationship; the acicular martensite a` and β phase maintain the Bragg orientation relationship. The inertial analysis plane is (334)β or (344). ) Β. 2.a" is found in Ti-Mo, Ti-W, Ti-Re, but not in Ti-V system; a" lattice parameter changes with composition; a" is the decrease in plasticity of titanium alloy.

Quenching ω phase formation: ω is a very small particle, which can only be observed by electron microscopy; ω increases the elastic modulus and hardness, and decreases the plasticity. The measurement of recrystallization mainly adopts the method of combining metallographic observation and X-ray diffraction. When recrystallization occurs, fine equiaxed grains appear on the deformed fibrous structure, and at the same time, the diffraction rings on the X-ray back-reflected Laue diagram begin to become unconnected spots. For heat-treatable β alloys, incomplete aging (500/4 to 8 hours, air cooling) can also be used to show the recrystallized structure, and the unrecrystallized grains after incomplete aging will appear dark after corrosion.
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