TZM Alloy Boat Molding Temperature

As we all know, the temperature has a great influence on the performance of metal. Generally, the processing temperature of metal is slightly higher than the ductile-brittle transition temperature, but below the recrystallization temperature. During TZM alloy boat manufacturing, should well control the molding temperature, which has a significant impact on TZM alloy boat’s properties. Its molding temperature is higher than the ductile-brittle transition temperature, but below the recrystallization temperature. TZM alloy has high melting point, high strength, good corrosion resistance and good high temperature mechanical properties, but it is room temperature brittle is large and high temperature oxidation resistance is poor, therefore it hard to machining. For this material, should process when the material has good plasticity, so as to obtain high-quality products.

Though stamping and welding TZM alloy plates can obtain TZM alloy boat, and it is essential to select the molding temperature in this process. When the material has good plasticity, which is easy to carry out the process, but also can obtain high-performance products. TZM alloy ductile-brittle transition temperature range is form -95 ℃ to -45 ℃. Its ductile-brittle transition temperature is below than room temperature, so the TZM alloy can be processed between room temperature and recrystallization temperature. The initial recrystallization temperature of alloy  is 1150 ℃. Alloy plate crack drawing depth was observed at different temperatures found alloy at 25 ℃, 100 ℃, 300 ℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃ and 1000 ℃ the crack drawing depth was 23mm, 32.5mm , 29.375mm, 42.16mm, 32.59mm, 31.15mm, 29.28mm, 16.73mm. The alloy crack drawing depth reached the highest value at 600 ℃, and therefore 600 ℃ most beneficial to the alloy plate plastic working. And TZM alloy boat material molding temperature is 600 ℃.

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Different Compression Ratio Affected TZM Alloy Plate Tensile Fracture

Observed 40%, 60%, 82% and 90% compression rate the TZM alloy plate tensile fracture morphology found as the compression ratio increases, the degree of densification is increase and the fracture mode change from the intergranular brittle fracture, intergranular ductile fracture, transcrystalline fracture to transgranular quasi-cleavage fracture.

The un-rollding alloy plate has a lot of voids and the fracture mode is intergranular brittle fracture. Observed the SEM picture can found each grain of alloy mostly is polyhedral shape and filled with voids. In the stretching process, these voids will become a source of cracks, causing fracture, reducing tensile strength.

When the compression rate is 40%, TZM alloy plate tensile fracture morphology is intergranular ductile fracture and cleavage fracture, in which a small number of grains have transgranular fracture phenomenon. There are some voids and small TiC particle. TiC particle showed in the grain boundary will reduce the strength of grain boundary. Further, presented crystal axis organization and voids will reduce the tensile strength of the alloy.

When the compression rate is 60%, the fracture mode is mixed fracture mode which includes quasi-cleavage fracture and transgranular ductile and brittle intergranular fracture. Besides, the dimple is clearly visible and transgranular fracture grains are increase, accompanied with quasi-cleavage fracture characteristics. In addition, the more transcrystalline fracture grains increases, indicating that the grain boundary of the alloy has been some strengthening.

When the compression rate is 80%, the fracture mode is still mixed fracture. However, transgranular fracture and quasi-cleavage fracture grains have further improved. In addition, the fibrous tissue of alloy is increase and you can clearly see some tearing ridge and shallow small dimple, which mainly occurs in plastic deformation of quasi-cleavage fracture. The alloy presented quasi-cleavage fracture has higher fracture toughness property.

When compression ratio is 90%, TZM alloy plate showing obvious quasi-cleavage fracture and transgranular fracture, most grain showing transgranular fracture. Further, since plastic deformation occurs in the grains and the cracks and voids are crushed and welded, so the welding and voids on the fracture have significantly decrease, which can enhance the strength and cohesion of the alloy, improving alloy’s mechanical properties.

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Different Annealing Temperature Affected TZM Alloy Plate Tensile Fracture

Observed at different annealing temperatures 80% compression ratio, 2.3mm TZM alloy’s tensile fracture morphology found the influence of annealing temperature on alloy’s tensile fracture (Fig.5-9). When the annealing temperature at 850 ℃, the tensile fracture of alloy is mainly transgranular fracture and there is significant cleavage steps on the fracture. In addition, there are a lot of voids in the fracture grain boundary. Besides, these holes will form the crack source stretching process, resulting alloy breakage.

After annealing at 1000 ℃, the fracture has obvious quasi-cleavage pattern river shape and cleavage steps. And this cleavage step formed in the process of crack propagation and dislocations cross-cut. Further, in the cleavage plane have some plastic deformation tearing ridge, so the alloy before breaking through a lot of plastic deformation rather than brittle fracture.

After annealing at 1150 ℃, the alloy fracture surface is similar with 1000 ℃ annealing fracture surface mainly quasi-cleavage fracture. The alloy having quasi-cleavage fracture the fracture plastic is better.

As we knew the recrystallization temperature of TZM alloy is about 1200 ℃. When the annealing temperature is 1300 ℃, the grains of alloy is more coarse and the fracture surface is relatively flat. And the fracture mode is mainly transgranular fracture and intergranular ductile fracture, indicated the plastic property has further improved. However, observed under 1300 ℃ annealing temperature alloy’s enlarged image found there has irregular particles and pits left by tensile fracture, as well as strengthening phase precipitated. This shows that when the annealing temperature is higher than the recrystallization temperature, it will weaken the dispersed phase and will reduce the mechanical properties of the alloy.

Therefore, during the stress relief annealing, the annealing temperature should be controlled below the recrystallization temperature. When the annealing temperature is higher than recrystallization temperature, although the plastic property is been improved, however the mechanical properties of the alloy is decrease.

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Rolling Affected TZM Alloy Plate Mechanical Properties

Compared before and after rolling TZM alloy plate’s room temperature mechanical properties found fine-grained sintered TZM alloy blank after appropriate deformation the density, strength and toughness have been improved to some extent. The tensile strength is greater than 840MPa and elongation is more than 4%. Besides the grain size is small. In TZM alloy Mo grains have weak bonding force, so under the small strain and lower energy it can easily to form cracking, having brittle fracture. And then after suitable rolling, the grains under pressure processing was elongated to fibrous and mutual effect and coexist with Mo grain, strengthening the binding force between the grains, reducing the sensitivity of the material to crack. Further, the grain has small size, at the same deformation degree the deformation can work in the more grains. Besides, the strain at the grains inside or near the grains is small difference and more uniform, reducing stress concentration, so that the material can withstand greater deformation before fracture. Fine grain size, grain boundary twists and turns is not conducive to crack propagation, so in the fracture process can absorb more energy, improving the elongation, exhibiting good room temperature toughness.

The deformation degree is an important factor influence alloy’s density and mechanical properties. In the rolling process, usually to express the deformation degree by compression ratio, the compression ration includes the overall compression ratio and compression rate pass and they have a great influence on the mechanical properties of the alloy. After rolling, the strength and elongation of TZM alloy will increase with overall compression ratio increase. In addition, when the different compression rate pass can reach to 80% overall compression rate, large compression ratio pass has good mechanical properties. This is mainly because large deformation and deformation speed is conducive to close the internal pores of sintered alloy blank, helping to eliminate and reduce alloy internal defects.

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TZM Alloy Plate Hot Rolling

Hot rolling is kind of roughing, whose main role is to make the alloy blank shaping, broadened and extended. Molybdenum has high thermal conductivity which can be quickly cooled in the air, so molybdenum plate can’t insulation and after cogging molybdenum plate blank should be heated, namely hot rolling. TZM alloy plate hot rolling temperature is higher than molybdenum plate, usually selected 1400 ℃as  hot rolling starting temperature, 50 minutes for heating time. Besides, during heating should employ uniform annealing process to alloy plate.

Hot rolling reduction is one of the important factors affecting the hot rolling process. In the hot rolling process, in order to improve alloy plate’s productivity and achieve uniform deformation should carry larger amount of reduction and increase passes. If the passes are small, the deformation does not get to the middle of the alloy plate, causing uneven deformation, resulting in alloy slab stratification.

In the hot rolling process, not only should consider the hot rolling reduction, but also consider the hot rolling finished temperature. The test found that the finished temperature have a greater impact on the organization and performance of the alloy plate, thereby affecting the performance of the finished product. When the finished temperature is higher than recrystallization temperature the grains along the machine deformation direction has some stretch, but the grain is coarse and in some areas shows equiaxed crystal phase. When finished rolling temperature is lower, the alloy plate shows smaller longitudinal axis compressed grain structure. This is mainly because molybdenum has higher stacking fault energy, so at high temperature deformation it is prone to slip and climb, while at the same time on the deformation took place dynamic recovery. Suitable finished temperature makes the alloy plate at high temperature recovery state, which is conductive to warm rolling. TZM alloy plate recrystallization temperature is higher than pure molybdenum, so the finished rolling temperature is generally higher than the pure molybdenum finished temperature about 200 ℃, and its finishing temperature is about 1200 ℃.

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TZM Alloy Plate Warm Rolling

TZM alloy plate after hot rolling, the fiber streamline structure has not yet formed. After hot rolling, manufacturers to carry out warm rolling process on TZM alloy plate can greatly improve the finished products rate. TZM alloy plastic-brittle transition temperature is closely related to the rolling temperature. Warm rolling is processing at the temperature which is under recrystallization, temperature and above ductility-brittle transition temperature. The warn rolling of molybdenum plate is generally processing under recrystallization temperature and above room temperature, having wide range. The molybdenum plate after rolling the fibrous tissue always is fibrous deformation tissue and there is a certain degree of work hardening. With the thinning of the molybdenum plate thickness, the rolling temperature should be gradually reduced. This is because as the deformation increase, the recrystallization temperature is decreased and molybdenum plate is very sensitive to the deformation temperature, so at a high temperature in a short time can produce recrystallization, and therefore the rolling temperature must be decreased. Compared to pure molybdenum, TZM alloy has higher recrystallization temperature, thus rolling temperature range is wider and it warm rolling temperature is about 1050 ℃. In warm rolling process, the amount of finish will reduce molybdenum and TZM alloy plastic - brittle transition temperature, improved low temperature ductility, and therefore the amount of deformation pass of warm rolling can not be too small, generally greater than 20%. Further, since the warm rolling temperature of the alloy plate has high heating temperature, after first heating the whole rolling deformation should not be too large, generally controlled at 20% to 30%, rolling passes generally not more than three times.

TZM alloy plate after high-temperature processing, there is low melting point volatile MoO3, molybdenum oxide particles and other pollutants on the surface of alloy. If you continue processing these pollutants will be pressed into the plate, causing defects on alloy plate surface. Therefore, in the rolling process requires an intermediate washing step. TZM alloy plate cleaning usually selected caustic fusion method.

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