TZM Alloy Oxidation Resistance Property

TZM alloy has good high temperature mechanical property, but at a high temperature oxidation resistance  property is poor. Under high temperature, it unable to form a protective oxide layer, so it must be used at high temperatures in non-oxidizing atmosphere. When the temperature is below 400 ℃, TZM alloy oxidation rate is very slow, because alloy surface formed less volatile MoO2. When the temperature is between 400 ~ 750 ℃, the oxidation rate becomes faster, the alloy surface to generate volatile MoO3. When the temperature is higher than 750 ℃, due to MoO3 volatile oxide weight decrease sharply.

Improving alloy’s oxidation resistance usually has two methods: alloying and coating method. Alloying method can not provide sufficient high-temperature oxidation resistance. Therefore the more commonly used method is coating method.

TZM alloy picture

There are many coating production process. The pack cementation method has many advantages including low cost, easy control, strong combination, so it has been widely used. TZM alloy coating by pack cementation method, generally choose Al powder as coating materials, NH4Cl as catalyst, Al2O3 as filler. The optimum parameters for the coating growth is tm (Al2O3): m (Al): m (NH4Cl) = 7: 2: 1,1000 ℃, 12h.

Observing XDR found that coating consist of Al5Mo, Al2Mo and Al2 (Mo4) 3 phase. Near the substrate the coating thickness is about 30um and average Al content is lower. Outer coating thickness is 20um and average Al content is higher. TZM alloy under coating protective within 10h operation, the oxidation rate is very fast. But within 10 ~ 50h, the oxidation rate becomes slowly, because the Al2O3-layer has a better protective effect and can prevent oxidation further development. It is shows coating method can well improve the oxidation resistance of the TZM alloy.

Email: sales@chinatungsten.com sales@xiamentungsten.com 

Tel.: +86 592 5129696/86 592 5129595

Fax: +86 592 5129797

TZM Alloy Thermodynamic Analysis

Using thermodynamic calculation found, TZM alloy during the sintering process, Ti, Zr and O reaction’s Gibbs energy is much lower than the binding energy of C and O, so Ti and Zr priority react with O to form TiO2 and ZrO2, reducing C’s deoxidize effect greatly. Further, since the strengthening elements Ti and Zr reacts with oxygen or nitrogen adsorbed in the compacted material, which also reduces the deoxygenation of C, so that the C content in TZM alloy is difficult to control.

In TZM alloy, strengthening elements titanium (Ti), zirconium (Zr) and carbon (C) will produce second phase strengthening and solid solution strengthening in the alloy. TZM alloy during sintering, the oxygen (O) in molybdenum powder will react with C to generate CO, and in this process C acts as a deoxidizer. In addition, C works together H2 protective gas to reduce oxygen content of the alloy.

TZM alloy picture

After thermodynamic analysis, Ti, Zr, Mo reacts with C to generate TiC, ZrC, Mo2C decomposed at elevated temperatures, dissolved into the molybdenum substrate. If the alloy O content is higher, there may occur the following reaction: Ti (Zr) C + [O] → Ti (Zr) nO2n-1 + CO2 or Mo2C + [O] → Mo + CO2. And this is the reason TZM alloy after high temperature treatment the second phases are all Ti and Zr oxides.

If TZM alloy oxygen content is too high, the oxygen will react with Ti, Zr to form the corresponding oxide, so a large number of second phase produce at grain boundaries and make mechanical properties of the alloy deterioration. Thereby controlling the oxygen content in TZM alloy has an important influence on the mechanical properties of the material guarantee. During the alloy production, to reduce the oxygen content of the TZM alloy, the most effective measure is to reduce the oxygen content of the raw material and production process oxygen content. So the manufacturers can use hypoxia molybdenum powder and vacuum mixing powder measure.

Email: sales@chinatungsten.com sales@xiamentungsten.com 

Tel.: +86 592 5129696/86 592 5129595

Fax: +86 592 5129797

TZM Alloy High Temperature Properties

TZM alloy has good high temperature property, so it can be made of high temperature components used in various fields. TZM alloy High temperature properties include high-temperature tensile property, high temperature oxidation resistance property, high-temperature fatigue property, and high-temperature bending and creep property.

TZM alloy picture

High temperature tensile property: High-temperature tensile property influence by many factors, such as different forms TZM alloy, TiC and ZrC doping method, production method and temperature. TZM alloy after deformation, as the temperature rises, the tensile strength decreased significantly. Zr alloy element added in pure Zr has best results, the amount of 0.1%, having highest performance. And Ti element added in TiH2 has best results, the amount of 0.8%, the alloy having better performance. Using powder metallurgic method and melting method to produce TZM plate the performance is equivalent, but the strength of TZM bars prepared by melting method was significantly higher than prepared by powder metallurgy method.

High temperature fatigue resistance: TZM alloy fatigue life at 500 ℃ and 350 ℃ has little difference, but at 500 ℃ fatigue life is slightly lower than 350 ℃. At 350 ~ 500 ℃, the thermal fatigue life of the alloy is significantly lower than the fatigue life at 350 ~ 500 ℃. This may be caused by the synthetic effect of temperature and cyclic loading, such that the fatigue life is lower than the thermal fatigue life. With the increase of the maximum cyclic stress, fatigue life shortening, elongation increased.

High temperature oxidation resistance: TZM alloy in high temperature oxidation rate is very fast, it can not generate antioxidant protection layer to protect itself. There are two methods for improving high-temperature oxidation resistance property which are alloying methods and coating method, and the coating method has better effect.

High temperature bending and creep property: TZM alloy creep is toward compressive strain direction, and when fatigue life reaches at 2% to 10%, creep direction changes to stretching strain. Creep property is closely related with stress intensity and temperature. Cyclic stress range increases, the more serious cyclic creep. With increasing temperature, cyclic creep has become more apparently.

Email: sales@chinatungsten.com sales@xiamentungsten.com
Tel.: +86 592 5129696/86 592 5129595
Fax: +86 592 5129797

Vacuum Arc Melting of TZM Alloy

There are two main methods for TZM alloy production: one is the powder metallurgy method and the other one is vacuum arc melting method. TZM alloy vacuum arc smelting process including: electrode production, water cooling effects, stable arc stirring and melting power. Good smelting process has a certain impact on the quality of TZM alloy. In order to produce good performance TZM alloy should be strict requirements on its smelting process.

TZM alloy picture

Electrode requirements: the ingredients of electrode should be uniform; electrode no bending, should meet the requirement of straightness; electrode should be dry, bright, no oxidation; electrode should tie up tightly.

Water cooling effect: in vacuum arc melting furnace, there are two mainly function of crystallizer water cooling effect: one is to take away the heat released during melting, making sure that crystallization will not be burned; the other is affecting the inside organization of ingot, which is heating ingot’s bottom and all around making ingot produced directional columnar grain structure. When melting TZM alloy, cooling water pressure controlling in 2.0 to 3.0 kg / cm2, the water layer about 10mm is best.

Arc stable stirring: during melting TZM alloy, to plus a coil parallel circling with crystallizer and, after powder on forming magnetic field. The main role of the magnetic field is constraining the arc and making the molten pool to solidify under stirring condition. The arc constraining effect is called "arc stable." In addition, to take appropriate arc stability magnetic field intensity can reduce crystallizer breakdown.

Melting power: the power of the melting means melting current and voltage, and it is important process parameters. Inappropriate parameters can cause failure of TZM alloy smelting. Selecting the appropriate melting powder is close related with electrical machine and crystallizer size. The "L" is refer to the distance between the electrode and the crystallizer wall, then the lower value L is, the greater coverage area of ​​the arc on weld pool, and at the same powder the pool heating state is better, the more active the pool. On the contrary, the operation will be difficult and crystallizer is easy to damage.

Email: sales@chinatungsten.com  sales@xiamentungsten.com 

Tel.: +86 592 5129696/86 592 5129595

Fax: +86 592 5129797

TZM Alloy Properties

TZM alloy picture

TZM alloy has many good properties, such as physical property, chemical property and mechanical property, including high melting point, high strength, high elastic modulus, small linear expansion coefficient, low vapor pressure, good electrical and thermal conductivity, high corrosion resistance and good high temperature mechanical properties , so it is widely used in various fields.

High temperature oxidation resistance property: TZM alloy has high melting point, so that it can be widely used in many field as a high temperature material. However, at high temperature, the alloy has poor oxidation resistance property can not form anti-oxidation layer to protect itself, so the oxidation rate is faster and service life is shorter at high temperatures. In order to improve high temperature oxidation resistance property of the alloy there are two methods: alloying and coating technology.

Room temperature and high temperature tensile mechanical property: Compared with molybdenum, TZM alloy room temperature tensile property is better, but not as good as the extension of molybdenum. Experiments show that at 1200 ℃, the tensile strength of molybdenum has been a significant decline, but the tensile strength of the TZM alloy remains at a high level. This is mainly because the second phase strengthening impacts TZM alloy’s property.

High temperature bending and creep properties: TZM alloy at high temperatures exhibited excellent bending property, but with temperature increase, the anti-bending property of TZM alloy is poor. TZM alloy creep property is related with temperature and stress intensity. With cyclic stress increasing, cyclic creep becomes more serious. In the same cyclic stress range, the temperature has large impact on creep property, as the temperature rises, the more obvious cyclic creep showing.

High temperature fatigue resistance: The study found that with the increase of the maximum cyclic stress, high temperature fatigue property continues to shorten, the elongation gradually increasing.

Email: sales@chinatungsten.com sales@xiamentungsten.com 

Tel.: +86 592 5129696/86 592 5129595

Fax: +86 592 5129797

TZM Alloy Properties Improvement

TZM alloy picture

TZM alloy has high temperature property, but at the high temperature oxidation resistance is poor. At the high temperature TZM alloy can’t produce anti-oxidation layer to protect itself, leading to life service and application range greatly shortened. Improving alloy’s oxidation resistance there are two main methods: alloyage and coating method. Alloyage refers to adding trace elements to improve alloy’s oxidation resistance. And coating method refers to coating a protection layer on alloy surface to improve high temperature oxidation resistance of the alloy. Al powder is usually used in coating material as raw material. And after experiment found the optimum parameters for coating are as following: m (Al2O3): m (Al): m (NH4Cl) = 7: 2: 1,1000 ℃, 12h.

Improving the ductile-brittle transition temperature and mechanical property of the alloy usually use neutron irradiation method. It was found that the alloy after neutron radiation, tensile property significantly improved, although the ductility is decrease, but the hardness is increase. At present, the study of neutron radiation is not mature and the general consensus is obtained through research, which is the radiation will have a lot of small gap in the alloy at a lower temperature, but high temperature radiation the gap will increases and DBTT will decrease.

Alloy after extrusion process will produce a lot of stress. The stress will largely affect the mechanical properties of the alloy. To change the annealing temperature can reduce the stress to improve its machinability. It was found that annealing temperature changes will affect alloy internal organization to cause alloy properties change. Overall, as the annealing temperature increase, the elongation of the alloy is increase and work hardening decrease. On the other hand, improving the production process and quality of raw material is good for TZM alloy properties improvement.

Email: sales@chinatungsten.com sales@xiamentungsten.com
Tel.: +86 592 5129696/86 592 5129595
Fax: +86 592 5129797