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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Vacuum annealing process of titanium alloy

Advantages of titanium and titanium alloys:

Low density, high specific strength, higher heat resistance than aluminum, and good corrosion resistance

Disadvantages of titanium and titanium alloys:

Poor thermal conductivity, poor wear resistance, low elastic modulus, high chemical activity

Characteristics of titanium alloy vacuum heat treatment:

(1) Martensitic transformation will not cause significant strengthening of the alloy

(2) The formation of w phase should be avoided

(3) Allotropic transformation makes it difficult to refine grains

(4)Poor thermal conductivity

(5) Chemically active

(6) There is a large difference in β phase transition points

(7) β grains have a greater tendency to grow when heated in the β phase region

Vacuum annealing process

Purpose: To reduce the hydrogen content in the surface layer of titanium alloy to a safe concentration and eliminate the possibility of hydrogen embrittlement. In addition, it can reduce residual stress and ensure the mechanical properties and service performance of the alloy.

Precautions:

Reduce the hydrogen concentration in the surface layer of the titanium alloy to a level that will not cause hydrogen embrittlement (chronic fracture) during subsequent use;

Reduce residual stress (especially welding stress) to a level that cannot negatively affect the service characteristics of titanium alloy components;

It is not allowed to guarantee the mechanical properties and performance of titanium alloy components, and unfavorable factors such as evaporation of alloy elements from the surface layer must be reduced to the minimum level;

Keep the annealed components to their original dimensions;

An oxide film is formed on the surface of vacuum annealed parts to prevent the metal from interacting with water vapor and other hydrogen-containing gases.

Influencing factors: annealing temperature and holding time

Main types of titanium alloy heat treatment

Enhanced heat treatment

Quenching aging is the main way to strengthen titanium alloy heat treatment, so it is called strengthening heat treatment. Strengthening heat treatment is an important way to improve the strength index of titanium alloy. Similarities and differences between titanium alloy strengthening heat treatment and steel and aluminum:

(1) Martensite can be obtained by quenching both steel and titanium, but the martensite of steel has high strength and strong strengthening effect, and tempering softens the steel; while titanium martensite has low hardness and little strengthening effect, and tempering makes the steel Alloy dispersion strengthening;

(2) Steel has only one martensitic strengthening mechanism, while the (α+β) titanium alloy with the same composition has two strengthening mechanisms. That is, the β-stabilizing element contained in the β phase during high-temperature quenching is less than the critical concentration, and the quenching transforms into martensite. body, martensite decomposes into a dispersed phase during aging to strengthen the alloy. During low-temperature quenching, the β phase contains stable elements greater than the critical concentration, and the supercooled β phase is obtained during quenching. During aging, the β phase decomposes into a dispersed phase to strengthen the alloy;

(3) The solution treatment and aging process of titanium alloys are basically similar to those of aluminum alloys. The principle of intensive heat treatment is to use rapid cooling to obtain metastable 3, a’, α phases, and then decompose them into dispersed α and β phases during artificial aging.

The alloy strengthening effect depends on the type, quantity, composition of the metastable phase and the dispersion of α and β phase particles formed after aging. The above is determined by the alloy composition and heat treatment process.

Typical defects caused by heat treatment of titanium alloys include the following:

(1) Produce coarse grains

(2) The mechanical properties and service performance of the alloy deviate from the established technical conditions

(3) Strong gas saturation

(4) Alloying elements evaporate from the surface or along the interface

(5) Distortion of parts or semi-finished products

(6) Cracks due to thermal stress and corresponding forces

Defect prevention:

The first 5 defects can be prevented and controlled through reasonable formulation and strict control of the vacuum heat treatment system; the prevention and control methods for the 6th defect are:

(1) Reduce the vacuum quenching temperature; (2) Increase the aging temperature; (3) Use isothermal quenching; (4) Introduce pre-high temperature aging before low temperature aging.