TZM Alloy Ti and Zr Determination by ICP-AES Method

In TZM alloy Ti and Zr content have great impact on its performance and through ICP-AES (Inductively Coupled Plasma - Atomic Emission Spectrometry) method can accurate measurement Ti and Zr content. ICP-AES has high sensitivity, high precision and wide linear working range and other properties, so it has widely application range.

Experimental Method: Weighed 0.2000g sample in 100ml beaker, added 2ml of sulfuric acid and 1g ammonium sulfate, and then placed on electric hot plate for heating. After the sample dissolved and cooled, poured into 100ml volumetric flask, diluted with water to the mark, for analysis.

Dissolving acid selection: The molybdenum alloy can dissolve by sulfuric acid - ammonium sulfate or nitrate - hydrofluoric acid mixture, but using nitric acid - hydrofluoric acid should ensure that sufficient amount of acid can make the sample completely dissolved. The viscosity of sulfuric acid is large, which is difficult to improve during lifting injections, but the amount is small, the results less affected. Overall consideration, the experiments will 2ml of sulfuric acid and 1g ammonium sulfate to dissolved molybdenum alloy.

Analytical line selection: To scan the spectral line by molybdenum, titanium, zirconium solution provided with the spectrum library, according to the shape of the peak, and condition of the peak value and matrix line to compare the interference of the matrix to the peak to chose small interference spectrum line, so choose 336.1nm as titanium determination spectral line, 343.8nm as zirconium determination spectral line.

Used ICP-AES method for Ti and Zr measurement and the values shows on the table. The recovery rate 98.33% -110.00%, RSD (n = 5) were less than 2.0%. This method avoids the conventional chemical analysis cumbersome process and greatly reduces the analysis time, which can simultaneously to measure Ti and Zr elements, so this method not only has fast, flexible and convenient features, but also can save a lot of manpower, reducing reagent consumption, improving the detection efficiency.

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Immersion Silver Graphite and TZM Alloy Dynamic Test

Material’s friction coefficient, wear rate and PV value determination is a complex process, not only related to material properties, but also related to wear surface relative motion, load size and characteristics and the surface quality and others factors. Dynamic test is a way to test product’s actual performance according to the material’s working conditions. It is different with normal room temperature test, which can observe product’s working condition reaction at high temperature, high-speed, high-pressure. Room temperature test is usually for material’s bending, compression, density and hardness and other properties test. Dynamic tests is not accurate than real machine test, but it is more economical and the test time is short compared to the real machine test shortened dozens of cycles, so dynamic test can not only save money, but also can provide faster required data.

Through dynamic test we can understand the immersion silver graphite and TZM alloy work condition, so the researchers carried out dynamic test on immersion silver graphite materials and grinding. It was found that, when the grinding appears grooves, burrs and other defects, it will destroy the graphite lubricating film formed on the working surface, resulting in friction and temperature increased, thus affecting material normal operation. Thus, grinding working surface roughness must meet the requirements of the drawing, and can not appear grooves, scratches, and other defects. In addition, before dynamic test, the sample should wear in under a certain pressure, so that there is lubricating film on the surface, which can reduce friction torque moment of starting and ensure the test can be carried out successfully.

In order to more economically and quickly understand the immersion silver graphite and TZM alloy working condition, so we can carry out dynamic test on immersion silver graphite material and grinding.

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Alloy Powder Affected TZM Alloy Rod Microstructure and Properties

Alloy powder will affect TZM alloy rod’s microstructure and properties, to choose high quality alloy powder and reasonable manufacturing technology can produce oxygen content of less than 0.03% and has excellent mechanical properties TZM alloy rods. 

TZM alloy rod production processes roughly as follows: mixing powder - pressing - sintering - forging - performance testing. During powder mixing, adding a certain amount of C powder in the reduction molybdenum powder and mixing with alcohol TiHx, ZrHx, it is marked for 1 *. Adding amount of C powder into reduction molybdenum powder and mixing with TiHx, ZrHx powder, it is labeled as 2 *. In unreduced molybdenum powder adding with a certain amount of C powder and alcohol TiHx, ZrHx, its number is 3 *. A certain amount of C powder and alcohol TiHx, ZrHx was added into unreduced molybdenum powder, its number is 4 *. Adding amount of titanium ball into 1 *, 2 *, 3 *, 4 * in V-blender continues to mixing for 24 hours. 

After mixing,manufacturers respectively load 1 *, 2 *, 3 *, 4 * into Ø130xL pouches and use 6000t cold isostatic press to press Ø126xL compacts. Use the same sintering process to sinter the compacts by 100kW medium frequency induction furnace to obtain sintered rods. The sintered rods forged by 750kg air hammer can obtain Ø57xL TZM rods. 

By observing TZM sintered rods scanning electron micrographs found that alloy powder containing alcohol TiHx, ZrHx alloy powder after sintering the distribution is more uniform. In addition, the reduction molybdenum powder can reduce the oxygen content of TZM rod. This is mainly because the reduction molybdenum powder combined partial oxygen will react with carbon to generate CO and CO2, and then be discharged, thereby reducing the alloy powder the oxygen content. Further, reduction molybdenum powder can also help to eliminate impurities in the powder, so that the chemical composition of molybdenum powder was purified and can eliminate molybdenum powder work-hardening to stabilize the crystal structure of the powder. 

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La-TZM Alloy and TZM Alloy Microstructure After Annealing

Using powder metallurgy method to produce TZM alloy and doped lanthanum (La2O3) TZM alloy (La-TZM alloy). Comparing these two kinds of alloys at 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃, 1500 ℃ and 1600 ℃ microstructure after annealing understand the effect of La2O3 on alloy recrystallization temperature.

Two types of alloys anneal at 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃, 1500 ℃ and 1600 ℃ with hydrogen atmosphere protection and the annealing time is 1 hour. After annealing the alloys operate tensile test. Finally, using optical microscope to observe and to analyze the microstructure of the alloy obtain its recrystallization temperature.

TZM alloy annealing at 1100 ℃, its structure has clear direction, but it is not obvious elongated cold processing streamline structure and processing streamline at high temperatures gradually becomes widen. At 1200 ℃, the alloy streamline in the grain boundary extension, a large number of irregular grains appear. Influenced by cold working, the grain aspect ratio is reduced, but still directionality. Annealing at 1300 ℃, grain aspect ratio is further reduced, but there are still significant directivity. Compared with 1400 ℃ annealing, annealing at 1500 ℃, the grains grow significantly and directional weakened. After annealing at 1600 ℃, the grains grow significantly, complete recrystallization has occurred.

La-TZM alloy after 1100 ℃ annealing, it has fine grain, but it doesn’t show obvious streamline processing structure. At 1200 ℃ annealing, alloy exhibits streamline processing and a number of grain closely spaced. Annealing at 1300 ℃, grain boundary becomes wider and fine grains is increase, having clear direction. Annealing at 1400 ℃ grain boundaries become wider and shows a lot of elongated fine grains. Besides, there are obvious signs of cold working. After 1500 ℃ annealing, grain orientation is significantly and elongation, but there have been a number of large chunks of the grain. On the other hand, affected by cold working closely spaced grains becomes less. After annealing at 1600 ℃, the grain shows equiaxed and grain size is finer, direction completely eliminated.

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La Doping Methods Affected La-TZM Alloy’s Properties

Doped with a certain amount of La2O3 during powder metallurgy process can obtain La-TZM alloy which has higher strength than TZM alloy. Different La doping methods have different effect on La-TZM alloy. Separately doped lanthanum by solid-solid doping method and solid-liquid doping  method, then after sintering, hot rolling, warm rolling, cold rolling and other processing procedures to obtain La-TZM alloy. Using solid-solid alloy doping method obtained alloy were labeled as 1# and solid - liquid were labeled as 2#.

Observed La-TZM alloy powder morphology and particle size distribution found that 2 # doping is more uniform more than 1# and there exists a local reunion phenomenon in 1#, form this we can see solid-liquid can obtain uniformly mixed material. After mechanical properties tensile testing found that La-TZM alloy tensile property is better than TZM alloy. Besides, 2# tensile property is superior to 1#, increased 10.9%. From this we will know solid-liquid is more conducive to improving the mechanical properties of the alloy. Analyzed La-TZM alloy SEM micrographs found the second phase in alloy not only distributes in the grain boundary, also distributes in the grain. And the average grain size of 2 # is less than 1 #. It is mainly because the powder which obtained by solid-liquid method is finer than solid-solid method and the finer powder, the smaller grain size is after sintering. In addition, there are a series of reactions of La2 (NO3) 3 at the beginning of sintering, so La2O3 mix more evenly. (La2 (NO3) 3 • 6H2O → La (NO3) 3 • 5H2O → La (NO3) 3 • 3H2O → La (NO3) 3 → LaONO3 → La2O3 • LaONO3 → La2O3).

The fracture morphology of solid-solid doped alloy plate and solid-liquid doped alloy plate is similar, but solid - liquid doped alloy plate fracture will be more careful and distributes fine and uniform second phase. The second phase is mainly distributed in the grain boundary and it can hinder the propagation of intergranular crack. Besides it has smaller crack and cleavage plane and it mainly shows intergranular fracture characteristics. Solid-liquid doping method second phase distribution is uniformly, and solid-solid doping method second phase has stratification phenomenon, so using solid-liquid can produce high quality and good properties alloy.

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TZM Alloy Second Phase Behavior Analysis

The strengthening elements Ti, Zr as carbides and oxides second phase exists in TZM alloy. TZM alloy is an deformation strengthening alloy, but solid solution strengthening and second phase dispersion strengthened alloy will deteriorate its pressure processing performance, so to study and to control the second phase behavior for improving the thermal deformation and properties of the alloy has great significance .

Analyzed alloy tensile fracture and impact fracture SEM showed that there are a lot of second phase at grain boundaries. In alloy carbon and oxygen content is higher (O: 0.08% ~ 0.09%, C: 0.04% ~ 0.05%), so many scholars believe that the second phase on the grain boundaries is Mo2C, (Ti, Zr) O and (Ti, Zr) C. In addition, in the tensile fracture, the researchers found in the grain boundaries and the grain there distributed second phase with different size and some second phases were abnormal thick. The second phase at the grain boundaries shows stretch dimple and between grain boundaries there is good plastic deformation connection. The second phase enriches at the grain boundaries. It is mainly because the sintered alloy in the cooling process the solubility of Ti, Zr and C in Mo was decrease, and therefore the second phase precipitation at grain boundaries. The large size second phase is Zr-containing carbides and oxides, because the sintering furnace cooling rate slowed down, so that the precipitation second phase can fully growth.

A large number of second phases exist in grain boundaries, due to elastic modulus differences, so the deformation can not synchronization, which will make grain boundary to break away form grains, crushing second phase, not only forming crack source, but also reducing the tensile strength and elongation. Further, intergranular second phase broken in the processing will reduce the workability and mechanical properties of the alloy.

Dispersed fine second phase in grain boundaries and in grains will help to improve alloy's recrystallization temperature and tensile strength, which is conductive to improving the properties of alloy. Second phase distribution usually depends on the thermal processing technology, if alloy is capable of rapid cooling and hardening during sintering, so that Ti, Zr and C can solid in Mo lattice, and then through tempered Ti, Zr and C precipitation to form dispersed second phase, witch can improve properties of the alloy.

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