TZM Alloy and Lanthanum Molybdenum Alloy

Molybdenum (Mo) has excellent high temperature strength, creep resistance, low thermal expansion coefficient, good thermal conductivity and corrosion resistance property, so it is widely used in the electronics industry, aerospace and military fields. However, Mo has a low recrystallization temperature, and therefore the application of pure molybdenum is often limited. Molybdenum recrystallization temperature is about 1000 ℃. Once molybdenum recrystallization, harmful impurity element is easy enrichment at the grain boundaries, thereby reducing the room temperature and high temperature performance of molybdenum. Alloying can help to improve the molybdenum’s high temperature properties. After alloying molybdenum alloy will produce solid solution strengthening and second phase strengthening, making the properties of the alloys has been improved. Analyzing lanthanum molybdenum alloy and TZM alloy’s high temperature performance plays an important role on molybdenum alloy further development.

Lanthanum molybdenum alloy and TZM alloy annealing at 1100 ℃, there are a small number of grains recrystallization, and with increasing annealing temperature, the recrystallized grains gradually increased. Recrystallized structure of molybdenum alloy exhibits elongated tissue which is different with pure molybdenum. Pure molybdenum is an isometric grain.

When the annealing temperature is less than 1400 ℃, lanthanum molybdenum alloy has a strong overall performance of strength and plasticity. When the temperature is higher than 1400 ℃, the tensile strength and ductility is decrease. TZM alloy’s tensile strength decreases with increasing temperature, but the plasticity increase, which is different with lanthanum molybdenum alloy. In addition, after comprehensive comparison, at the same temperature TZM alloy high temperature performance is better than lanthanum molybdenum alloy.

When the annealing temperature is higher than 1400 ℃, lanthanum molybdenum alloy exhibits hot brittleness which is different from the TZM alloy. This is mainly because, as the annealing temperature increase, the flow-line organization of lanthanum molybdenum alloys has a tendency to fracture. However, TZM alloy, whether in process state or recrystallization state, the size, shape and distribution of second phase are not significant changes.

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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.

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.

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Using TZM Alloy to Produce Titanium Isothermal Forging Mold Material

Titanium alloy has some special requirements on isothermal forging, for example, there are some special requirements on mold temperature, pressure and dwell time. During isothermal forging the mold temperature should be at 850~950 ℃ and pressure should be control at 100~120 MPa. Besides, the dwell time should be at 5~15 minutes, and based on the above requirements, commonly used nickel-base superalloy, insoluble metals and their alloys (TZM alloy), ceramic material, such as silicon nitride, silicon carbide and so on as titanium isothermal forging material. The experiment found that compared to the performance of other material TZM alloy has more favorable advantages. TZM alloy not only has good temperature resistance and high strength property, but the die service life also has a strong advantage.

Using TZM alloy as sophisticated forgings materials during isothermal forging, there may be has some crack happening in forging die to cause damage, and forging die damage may be caused by the following reasons:

1. The forging die happen some local plastic deformation and dimensional change;

2. Effected by the lubricant and protective gas, the embedding of material cause wearing;

3. The cracks concentrated on the place where the local stress is highly.

In order to prevent forging die early damage, understanding the carrying capacity before the crack spread of TZM alloy forging die, understanding of the conditions of forging die appeared, have important significance for judging the operation reliability and evaluation the forging die service life.

The cracks in the forging die are often unavoidable, so to slow the pace of cracks expansion has a certain influence on the service life of the mold. It was found that if the dwell time is too long, there will have a certain impact on crack formation and expansion. So isothermal forging pressing time should be as short.On the other hand, forging die at preheating and cooling will produce high thermal stress, causing cracks. In order to avoid large thermal stress, people should pay special attention to preheat uniformity.

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TZM Alloy Hot-dip Aluminum Coating Microstructure

TZM alloy has good high temperature performance and mechanical properties, often as heat-resistant and high-temperature structural materials widely used in nuclear reactors, aerospace, power generation and chemical industry, but it is easily oxidized in air at high temperature, thus greatly limiting its applications. Use hot-dip aluminized process to produce aluminum layer on TZM alloy surface, which can improve the high temperature oxidation resistance. After 800 ℃, 100h cyclic oxidation experiment found that TZM alloy surface coated on aluminum layer its high-temperature oxidation resistance is greatly improved. The coating consists of surface pure aluminum alloy layer and inner alloy layer and the mainly metallurgical of alloy layer is Al4Mo and Al5Mo phase.

TZM alloy after hot dip aluminum coating, its surface shows shiny metallic luster and surface is roughness, seamless plating. Observed alloy hot dip aluminum coating microstructure found, after hot dip aluminum coating the metallographic structure of alloy includes brown inlay, pure aluminum layer (I), alloy layer (II) and matrix (III). Besides, the coating is uniform and compact, divided into outer and inner layers, distinct phase interface. In addition, the study found that, at the same temperature of hot-dip, longer dipping time, the thickness of the alloy layer also increases.

Measured aluminum coated layer cross section microhardness found that the outer surface has lower hardness. When the hardness of load is 25g, the hardness range is HV30 ~ 130, which is mainly dependent on α-Al. With distance from the surface increasing, the hardness also increases. In 120um, the hardness value reaches HV760. In 120 ~ 150um, hardness changes at the range of HV760 ~ 758 and the hardness load is 500g, mainly because alloy layer Al4Mo and Al5Mo is cemented carbide phase having greater hardness. Then, as the distance further increase, the hardness begins to decline sharply, remained steady at HV260, where the hardness load is 100g and TZM alloy matrix hardness is HV260.

TZM

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Titanium Zirconium Molybdenum Ternary Alloy - Oral Planting Material

Titanium zirconium molybdenum ternary alloy (Y30) is an excellent performance oral planting material. The main ingredient is titanium (Ti), in order to improve overall performance on its basis doped with 5% zirconium (Zr) and 2% molybdenum (Mo). Zirconium is a neutral element, and its solid solution strengthening effect can improve the strength of Ti, molybdenum doped mainly to improve the tensile strength and corrosion resistance of titanium. In addition, doing polarity toxicity test, accumulation toxicity test, rat bone marrow cell chromosomal aberration test, pyrogen test, hemolysis test in vitro Chinese hamster ovary cell proliferation and other tests on titanium, zirconium, molybdenum found that the elements is security, non-toxic elements and has good biocompatibility as well. At the same time, doing the test of the physical properties, mechanical properties, and corrosion resistance found that titanium zirconium molybdenum ternary alloy is a safe and reliable oral planting material which has broad application prospects.

In order to evaluate the toxicity and safety of Y30 were done six biological safeties testing, and test reports are as follows:

1. Y30 leach liquor extract polar toxicity test: Using Y30 leach liquor injected the abdominal cavity of mice was observed after 14 days. The mice's diet, sleep, activity and growth are normal. The leach liquor is non-toxic to mice.

2. Y30 leach liquor accumulation (subacute) toxicity test, 25 days in a row using Y30 leach liquor injected mice, the cumulative amount reached 700cc / kg, the mice showed no death. It is shows that there is not cumulate effect on mice’s body.

3. Y30 leach liquor on rat bone marrow chromosome aberration test found the bone marrow cells of mice chromosome no effect chromosomal aberrations occur.

4. Y30 pyrogen test: injected rabbits with Y30 leach liquor after body temperature test found rabbit body temperature raise were below 0.6 ℃, in line with pyrogen test requirements.

5. Y30 hemolysis test: observe containing Y30 leach liquor of red blood cells found no fracture phenomena which described Y30 leach liquor afford hemolytic reaction.

6. Different concentrations of Y30 leach liquor in vitro hamster ovary (CHO) cell proliferation text: Y30 leach liquor does not affect the growth of CHO cells and it is kind of safe metal planting material.

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Surface Oxidation and Segregation of TZM Alloy

Segregation phenomenon refers to the constituent elements of the alloy uneven distribution in the crystallization. The experiment found that TZM alloy added element segregation occurs at ultrahigh vacuum and at different temperature ranges. Titanium segregation starts from 840 ℃ and zirconium segregation is beginning from 1100 ℃. Titanium’s maximum temperature segregation is 1150 ℃ and zirconium is 1350 ℃. Higher than the above temperature, the surface concentration of titanium and zirconium are decreasing, and higher than 1400 ℃titanium will disappear the same surface. Segregation temperature is similar to the required temperature of these two elements diffuse to the molybdenum substrate. The temperature of segregation disappearance depends on the balance of the additional diffusion kinetics.

In TZM alloys, titanium and zirconium element has a great affinity for oxygen, so oxidation reaction with oxygen is easily. Stability of TiO2 and ZrO2 promotes the surface material to absorbent the oxygen, free standard enthalpy of formation of these two oxides is lower than MoO2, and both vapor pressure is smaller than MoO2. Thus, the surface oxygen can diffuse to the alloy and preferential oxidation with the additive of alloy producing oxides precipitate. TZM alloy samples after 1390 ℃ treatment, the alloy surface is covered with a large amount of oxide precipitation. After milling alloy surface, the inside oxygen precipitates content only one-tenth of alloy surface.

We can confirm TZM alloy surface oxidation by microstructure oxide precipitation tests of the alloy. The shape and form of oxide precipitates has big difference with carbide precipitate. In an oxidizing atmosphere, at 1200 ℃ alloy starts decarburization reaction, oxygen is gradually dissolved and the original oxide oxidation occurs.

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