Powder Metallurgy (PM) Prepared Tungsten Copper Functionally Graded Materials(W/Cu FGMs)
Powder Metallurgy (PM) is a common,main method of preparing tungsten copper composite materials.However,the traditional PM is difficult to prepare dense W/Cu FGMs,therefore it shoul be improved. The improved method are including:
1.Hot pressing method
Mixed the different proportions powders,then superimpose and put the mixed powders into the mold cavity in proper order,to mold it then get the compact bodies and put them into the hot furnace sintering.Finally,passing the argon gas to prevent oxidation.Because the pressing process and sintering process could be carried out simultaneously when using hot pressing method,therefore,it can promptly reach the pleased density which cold pressing sintering can’t reach,under a lower pressure.Hot pressing method can be easy to controll the tungsten, copper ingredient and thus to prepare the different ratios of tungsten copper composite materials with high density and high formed flexibility. But the disadvantage is that the equipment need costs to much high cost,the components distributed unevenly,which is not conducive to mass production.
2.Extra high voltage gradient sintering method
This method is to mix the obtained fine tungsten,copper powders,then superimposing and molding the mixed powders according to the design components,after that,sintering pressuried in the extra high voltage electric sintering apparatus.During sintering process,you can add a sintering additive such as Ni to improve the material density and thermal bonding strength,but the thermo-physical properties of tungsten will also be evolved.For this reason,it’s not an ideal method for promoting the sintering of pure tungsten extremity.Therefore in this method,eliminated the use of sintering additives. Test results show that,the density of the five layers W/Cu FGMs which prepared under the certain pressure conditions,showed a gradient changing could be up to 97%,the density of pure tungsten layer is also up to 96%.
3.MBE molding method
The researchers combined the MBE molding method,particles size ratio and hot pressing solid phase sintering method,prepared W/Cu FGMs,nearly full densification. Every layer relative density of W/Cu FGMs prepared,reached more than 98%,thermal layer reached 99.9%.Moreover,each layer has regular shape, uniform thickness and clear interface between the layers position.And it’s successful to solve the problems of the imprecise controlled thickness of various graded layer and low efficiency of superimposing method.
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