Properties of niobium zirconium alloys

Nb-1Zr, Nb-10Hf-1Ti-0.7Zr and Nb-5Zr are three typical niobium zirconium alloys, which belong to niobium alloys with low strength and high plasticity. The properties of the above three typical niobium alloys are analyzed as follows.

(1) Nb-1Zr alloy is in the addition of about 1% zirconium, zirconium content in 0.8~1.2%, in addition to the alloy also contains 0.001% carbon, belongs to zirconium element strengthening and carbide precipitation alloy. Its crystal structure is a body centered cubic structure, at room temperature to most organic and mineral acids are not reactive, but dissolved in hydrofluoric acid and hydrofluoric acid and nitric acid mixed solution, when the temperature exceeds 100℃, its corrosion resistance to acid weakened. The oxidation resistance of Nb-1Zr alloy is good, and it is hardly oxidized at room temperature. The oxidation rate of Nb-1Zr alloy ingot is 7.1mg cm-2.h-1 when the temperature reaches 600℃, and the oxidation rate increases rapidly to 64.8 mg cm-2.h-1 when the temperature reaches 689℃.

In addition, 1% zirconium in Nb-1Zr alloy can also play a role in grain refinement. In order to produce high quality Nb-1Zr alloy wire and strip, it is often necessary to improve the processing rate and adopt the processing technology with a large amount of deformation. The grain size of 10~20μm can be obtained. At high temperature, the catalytic tendency of Nb-1Zr alloy is smaller than that of pure niobium. This is because the reaction between zirconium and niobium interstitial element oxygen atoms generates a large number of ZrO particles. These large number of second phase particles are dispersed in the energy, which inhibits the grain growth rate of the alloy, and plays the role of dispersion strengthening, improving the stability of the alloy at high temperature. After recrystallization heat treatment, the tensile strength of Nb-1Zr alloy at room temperature :345MPa, yield strength :255MPa, elongation :15%, extension-brittle transition temperature :-196℃, the alloy strength decreased significantly under high temperature conditions, tensile strength :186MPa, yield strength :165MPa, elongation :30%. The hardness change of Nb-1Zr alloy is related to temperature and processing quantity. Take Nb-1Zr alloy plate as an example, the Vickers hardness of Nb-1Zr alloy plate decreases rapidly from 110HV to about 50HV when the temperature increases from 0℃ to 300℃. When the temperature continues to rise from 300℃ to 600℃, the Vickers hardness does not change much. When the temperature continued to rise to 800℃, the Vickers hardness slightly increased to about 80HV, and as the temperature continued to rise to 1000℃, the Vickers hardness decreased to below 60HV. In addition, the amount of processing on the hardness of Nb-1Zr alloy also has a great influence, also take nB-1Zr alloy plate as an example, the cold working rate from 0 to 80% increase, the increase of hardness will be parabolic upward growth; When the processing rate is 20%, 40%, 60% and 80%, the vickers hardness of the processing state should be 125HV, 140HV, 150HV and 158HV; However, after annealing at 1204℃ and holding for 1 hour, the hardness of the processed Nb-1Zr alloy sheet will greatly decrease in the range of 80~100HV.

(2) Niobium C-103 alloy in the United States, the grade is C-103, is in niobium adding 9~11% hafnium, 0.7~1.3% titanium, ≤0.7% zirconium. The active elements hafnium and zirconium react with the carbon in niobium to form carbides, which play a dispersion strengthening role in the alloy. At the same time, hafnium and zirconium react with oxygen in niobium to form oxides, which can precipitate and strengthen the alloy. And hafnium plays a role in improving the weldability of the alloy.

Taking niobium C-103 alloy sheet as an example, the mechanical properties of the cold-worked sheet are tensile strength :724MPa, yield strength :665MPa, elongation :4.5%; After annealing at 871℃ and stress-relieving heat treatment for 1 hour, tensile strength :645MPa, yield strength :607MPa, elongation :9%; After annealing at 1316℃ and recrystallization heat treatment for 1 hour, the tensile strength is 420MPa, the yield strength is 289MPa and the elongation is 25%. The mechanical properties of Nb-10Hf-1Ti-0.7Zr alloy sheet decreased rapidly at high temperature, especially when the temperature exceeded 1300℃. The mechanical properties of the alloy sheet at 1371℃ were as follows: tensile strength :89MPa, yield strength :73MPa, elongation :70%.

Nb-10Hf-1Ti-0.7zr alloy has high ductility, good cold working deformation property and high temperature specific strength. But the high temperature oxidation resistance is poor, the temperature is higher than 1300℃, the slow speed of the air flow after 0.5 hours, its oxidation degree is very serious, there will be a large number of white oxide generation, and it is easy to peel off from the alloy, so the use of high temperature conditions, must be antioxidant coating. Under the protection of anti-oxidation coating, Nb-10Hf-1Ti-0.7Zr alloy material can be used at about 1200℃, and has good weldability and coating performance. It is widely used in the nozzle extension of aerospace engines and the combustion chamber throat of attitude adjustment engines. With the rapid development of aviation, space industry, more and more high to the requirement of high temperature niobium alloy material, high temperature niobium alloy research direction at present basically has two aspects, one is decreasing the density of niobium alloy, high temperature is lighter, niobium alloy in of niobium alloy solid solution strengthening elements in most of them are high density of metal, For example, tungsten, molybdenum, tantalum, zirconium, hafnium, and other metals are much denser than silver, and the addition of these heavier metals makes niobium alloys denser; Second, the high temperature strength and oxidation resistance of niobium alloy is put forward higher requirements, the temperature range of 1600~1800℃, niobium alloy material still has good strength and oxidation resistance.