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Using Brazing Titanium Graphite and TZM Alloy to Produce Joint

Graphite is a low atomic weight materials, having low loudness density, high sublimation point (3850 ℃), high thermal conductivity, heat capacity and excellent impact resistance and other advantages. To produce a new type alloy material and this alloy is maked up by graphite W and Mo. As we know, graphite has good thermal performance and low-density advantages and other advantages. So doped with graphite into Mo or W to produce new type alloy is good for heat dissipation, but at the same time will reduce products’ quality, especially in some of the high-speed rotating components. Doped Ti, Zr and other trace elements in Mo, after powder metallurgy process and alloying process can produce Mo alloy, which is TZM alloying. And TZM alloy has good mechanical property, thermal physical property, thermal and electrical conductivity which is higher than other insoluble metal. Using TZM alloy and graphite to produce composite joints obtained by braze welding has widely applications in the aerospace field. Vacuum brazing is the preferred process for preparing high temperature composite joints. China domestic current has little research in this area. Smid, who studied the Mo-graphite composite materials for NET / ITER nuclear reactor to obtain joint which can use in 800 ~ 1200 ℃. Chan, who use 72Ag-28Cu and 95Ag-5Al brazing filer metal for Ti-6Al-4V and TZM alloy brazing, and the brazing temperature is 850 ℃ and 950 ℃. Besides, the weld of joint is good.

TZM alloy composition is (mass fraction, %) 99.4Mo-0.47Zr-0.1Ti, the rest is other trace elements. And the diameter is 100mm. After powder metallurgy sintering and 1400 ℃ forging, upsetting annealing can obtain TZM alloy. Graphite has high strength, high density, high purity, and its outer diameter is greater than 100mm. TZM alloy and Ti foil washed by ultrasonic with acetone, is placed in vacuum hot pressing brazing furnace sequentially. Chose titanium foil as brazing filler metal, and titanium foil thickness is 0.05mm and diameter is 100mm.

After brazing, under optical microscope and stereo microscope specimens found the joint is densification and has uniform width. The joint observed by SEM and microanalysis component analysis (EDX) showed that the brazing layer width is about 120um and complete penetration rate is above 95%, which has clearly two-layered structure. Graphite matrix is ​​loose, the brazing layer closing to graphite substrate side has deeper color. This is interface reaction layer produced by graphite substrate and brazing filler metal chemical reaction. This layer connects with graphite, so it is relatively smooth. Besides, there are a small number of cracks and voids. And the thickness of reaction layer occupies 1/3 of the entire brazing layer. Analyzed by EDS, the average component of mixed layer is (mole fraction, %) 46.22C-53.78Ti. And the mix layer is mixed by high melting point TiC and rest of brazing filler metal which is produced by interfacial reaction. The brazing layer closing to TZM matrix the color is lighter. This brazing layer is Ti-Mo solid solution, which accounted for 2/3 of the entire solder layer. Combined with TZM substrate, the structure is smooth, and there are knife-like carbide to grow up, improved joint performance. The EDS average component (mole fraction, %) is 51.48Ti-48.16Mo.

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