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Study The Properties Of Fe-based Amorphous Alloy And Composite Powder By Laser Cladding

Posted on:2017-03-09Degree:MasterType:Thesis
Country:ChinaCandidate:M W WangFull Text:PDF
GTID:2271330485467105Subject:Mechanical Manufacturing and Automation
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With the rapid development of the modern industrial technology, mechanical parts require the ability to continue to work at high temperatures, high pressure, and corrosion environment, which demand the higher requirements for the surface properties of the parts. Improve the surface properties of parts, not only to extend its life, but also to create huge economic benefits. Fe-based amorphous alloys have high strength, excellent wear resistance, corrosion resistance, which has a broad application in improving the surface properties of the parts. Laser cladding technology as an important method of surface modification and rapid prototyping, which has high production efficiency, low cost, good quality of the coating, etc., are widely used in aerospace, automotive, petrochemical, and other fields. Fe-based amorphous and composite coating was prepared on the surface of parts with laser cladding, which can significantly improve the mechanical and corrosion properties of the parts.In this paper, two kinds of composition design principle is used:The first one is a new composition design concept "near the formation enthalpy" to design all-metal elements FessNb15Ti15Ta15 amorphous alloy. The second one is the composition design of composites, which adds a different content of TiC of 5%,10%,15%and 20% into FessNb15Ti15Ta15 amorphous alloy as an enhancement phase. The purpose of addition is to improve the room temperature plastic of the Fe-based amorphous alloy, and to improve the mechanical properties of the coating. The Fe55Nb15Ti15Ta15 amorphous alloy powder and the composite powder were prepared by mechanical alloying. In the process of ball mill, the amorphous process of powder, phase transformation, microstructure and thermal properties were analyzed. Then after the ball milled powder was used for laser cladding. The different process parameters effect on the macro quality, microstructure, mechanical properties and corrosion resistance of the cladding layer were discussed.The results show that:"near the formation enthalpy" composition design is feasible. The designed Fe55Nb15Ti15Ta15 alloy powder transformed into a fully amorphous state after ball milling of 80 h. TiC addition retarded the process of amorphous, refined crystalline grain of powder, and finally obtained the amorphous alloy matrix composite. Amorphization mechanism is that under the continuing applied mechanical energy which provided by the colliding balls, each element generated diffusion solution and made a serious distortion of the lattice. When the distortion energy exceeded the critical value of free energy of amorphous, the lattice collapse, and eventually formed amorphous. The milled powder has a similar shape in spherical, with good liquidity. TiC addition did not change the thermal properties of amorphous alloy powder, two kinds of powder has a wide supercooled liquid region (112 ℃) and the type of crystallization is eutectic, which is a good alloy powder for laser cladding.In the laser cladding process, the laser power P, the scanning speed V, the distance of laser head between the coating H, which have a significant effect on the microstructure and macro mechanics, corrosion resistance. In this paper, based on previous experimental results, the single factor analysis of V was optimized. The optimum process parameters is P=350 W, V=240 mm/min, H=24 mm. The cladding layer with the substrate produced a good metallurgical combination, no obvious bubbles, cracks and other defects. The obtained coating is mainly composed of Fe2Ti, Ta0.15Ti0.85, Fe and uncertain phase. The average hardness of the cladding layer is 643.3 HV, average coefficient of friction is 0.2996, and corrosion potential is-0.5896 V, which is superior to the matrix material.TiC addition changed the microstructure of the cladding layer, and improved the properties of the coating. TiC addition refined the microstructure of coating and increased the amount of amorphous phase. The microhardness of coatings increased with the increment of TiC, when TiC content was 20%, the coating has the maximum average microhardness of 747.6 HV. But the friction coefficient presented a irregular change with the increment of TiC. Compared to the amorphous alloy powder coating, the coefficient of friction is reduced, indicating improved abrasion resistance of the coating. TiC addition also improved corrosion resistance of the coating, when the TiC content was 20%, the coating has the best corrosion resistance.
Keywords/Search Tags:Fe-based amorphous alloy coating, Mechanical alloying, Laser Cladding, Mechanical properties, Corrosion resistance
PDF Full Text Request
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