| Tungsten-based high density alloy is an important part of tungsten alloy materials, is an important raw material and one kind of strategic resource for national defense and nuclear industry. At present the main method of preparation is powder metallurgy sintering, but it’s limited by sintering equipment size and sintering temperature, so there are still some problems in the preparation of tungsten alloy parts with high performance and large size, which limits the application in national high-end nuclear industry. Whereas the laser solid forming technology, which is based on the additive manufacturing, provides a new way for the preparation and forming of tungsten-based high density alloy parts, if we can use this technology into the production and preparation of tungsten-based high density alloy, it will be of great significance in practice.We carried out a series of preliminary technical exploration of tungsten-based high density alloys which are fabricated by laser solid forming technology, including the comparison of single-route claddings W60 alloy and W93Ni4.5Fe1.5, the deposition and analysis of single-route but multi-layer claddings about W-Ni alloy, the preliminary exploration of W-Ni-Fe alloy fabricated by laser solid forming and the forming of W-Ni-Fe and Ni25 powder surface objects; In addition, we also used finite element analysis to study the temperature field changes during the 3D forming process, used computer numerical simulation to study the influence of tungsten content and void ratio on the property of alloy. Finally, we almost worked out a series of laser solid forming alloy parameters, to achieve a simple forming of alloy about W-Ni-Fe, and studied the relation between micro structure and properties after forming, laid the foundation for more deeply research. The main results we got are as follows:1.For both W60 alloy and W93Ni4.5Fe1.5 alloy, when single track laser cladding, the appropriate parameters are:The laser power is 1400W, the diameter of laser beam spot is about 2mm, and the scanning speed is about 2mm/s, thus the cladding effect is the best; The multilayer solid forming effect of sample W90Ni10 is good, which is of bright and pale surface, with a gray color, the fracturing strength is up to 882MPa.2. To use computer numerical simulation to study temperature field changes in the three dimensional accumulation process, ensured the temperature distribution in laser cladding process and the region of high temperature gradient, found that there exist heat accumulation phenomenon in cladding layers during the laser cladding process, and big thermal gradient occurred between the cladding layer and the baseplate layer; To analyse the influence of tungsten’s content (40%,50%,60%, 70%、80%'90%) on the mechanical properties of the alloy forming sample, found that with the increasing of tungsten content, the yield strength of alloy increased, the elastic modulus increased, but the ductility decreased. Through these researches, to master some forming effective regulations, to lay the foundation for the later tungsten alloy fabrication.3. The forming parameters are:The laser power is 1400W, the powder feeding rate is 0.2 rpm, the scanning speed is 5 mm/s, the laser beam spot diameter is 2mm, the laser height is 15mm, the pressure of protective gas is 0.04 MPa, the overlap ratio is 40%. To prepare various proportions of W-Ni-Fe high density alloy mechanical tensile test pieces under atmospheric conditions, by testing the tensile strength and hardness, analyzing the micros tructure and proportions of the components, the results show that there are still some difference from the traditional powder metallurgy sintering process in terms of formability and mechanical properties, whose maximum tensile strength reaches 717.5MPa at W60, then with the increase of W atom proportion it significantly reduced instead, when the proportion of W atom is more than 80%, the strength is lower than 400MPa. The analyses show that holes and oxidation phenomenon exist in the samples, a large number of W doesn’t melt, the more of Ni, Fe elements, the uniformity of microstructure is better, the composition segregation is smaller; To analyse and calculate the effect of void ratio(0.5%,1%, 1.5%and 2%) on the mechanical properties of the alloy forming specimen, found that tungsten particles carried the main force, there were many stress distribution areas near the holes, and these areas were also loaded a maximum force, produced fracturing firstly. And with the increasing of porosities, the maximum stress of matrix phase remained unchanged, just the stress distributions changed, the areas became more and more.4. To make use of the three-axis robot arm, matched with the rotation of the turntable and the X-Z plane right angle rotation, predefine coordinate trajectory parameters, to make out a variety of Ni25 surface objects formed by laser solid forming technology, their forming effects are perfect, the external configuration is continuum, and no obvious defects can be observed. Laser microscope observation find that the structure is compact, no obvious cracks and holes; Then we carried on the fabrication of tungsten heavy alloy surface objects formed by laser solid forming, through multi-round experiments to optimize the process, finally we got W60 surface object, and the forming effect was perfect. |
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