| In this paper, Ti powder, Al powder and B powder were used as raw materials, and were mixed by the composition of Ti-7Al-x B(x=0, 0.2, 0.4, 0.6 wt.%).Then the mixed powder was ball milled by a double tank 3d swing ball mill at a speed of 400r/min. The morphology and phase composition of powder particles were analyzed using X-ray diffraction(XRD)and scanning electron microscope(SEM) after ball milled for 5 h,10 h,15 h and 20 h respectively. The powder after 20 h ball milling was sintered in vacuum hot-pressing furnace(heating temperature 1100℃,holding time 1h, 30 MPa pressure,). The regularity of phases composition, micromorphology of the strengthening phases,the density and hardness of the sintered samples were analyzed about the different composition alloys. MG-2000 friction and wear testing machine was used to study the wear resistance and wear mechanism of Ti-7Al-x B alloys under the load of 20N、30N、40N、50N conditions. Wear mechanism of prepared alloys were discussed. High temperature oxidation property was tested using the box resistance furnace at 900 ℃. The high temperature oxidation properties of Ti-7Al-x B alloys were analyzed at the aspects of thermodynamics and dynamics.High-energy ball milling results show that: Ti-7Al-x B mixed powder after high-energy ball milled for 20 h, the powder particles were refined to about 5μm, and the powder particle sizes did not decrease obviously with the a of B elements. XRD analysis shows that part of aluminum was solid solution into the titanium lattice during the ball milling process. From SEM results, after the powder was refined, it turned into layer-shaped structure, and Ti B phase were generated, indicating with the grains refining,the mechanical alloying occurred during the ball milling process.Vacuum sintering experiment results show that: Ti-7Al-x B alloys densities were above97%, and the microstructure is homogeneous, Ti B is in typical whisker shape. After adding0.2wt.% boron, the alloys grain sizes are refined, grain refinement was not obvious with further increasing boron content, the reason was that Ti B hindered the growing of matrix grains. Addition of boron significantly improves the density and hardness of Ti-7Al alloy,but with the increasing of boron content, the density of the alloy has a slight decrease.Dry friction and wear test results show that: within the scope of 20N~50N loads, the friction coefficient of Ti-7Al-x B(x=0.2, 0.4, 0.6wt.%) alloy were lower than that of Ti-7Al matrix alloy under the same load, the friction coefficients didn’t appear to be much different from containing different percentage of element Boron. Friction coefficients of Ti-7Al matrix alloy increased with the increasing of loads, while friction coefficients of Ti-7Al-x B(x=0.2, 0.4, 0.6wt.%) alloys decreased with the increasing of loads. The wear resistance of Ti-7Al-x B(x=0.2, 0.4, 0.6wt.%) alloys were better than Ti-7Al matrix alloy. When the load increases from 20 to 50 N, the wear mechanism of Ti-7Al matrix alloy changes from mild adhesive wear to serious adhesive wear. Under the heaviest load, the wear mechanism of Ti-7Al-x B(x=0.2, 0.4, 0.6wt.%) alloys are including mild adhesion wear, oxidation wear and abrasive wear.Test results of constant temperature oxidation at 900℃ show that: After 100 h high temperature oxidation test, the oxidation mass gain curve of Ti-7Al-x B(x=0.2, 0.4, 0.6wt.%)alloys rises slowly and the oxidation layers thickness of sample decreased with the increasing of Boron element compared with Ti-7Al matrix alloy. Oxidation products of Ti-7Al matrix alloy were mostly Ti O2 with prismatic structure, the surface oxides of Ti-7Al-x B(x=0.2, 0.4, 0.6wt.%) alloys are composed of continuous Ti O2 and Al2O3 mixture which are finely grained and compact distributed on the surface of the prismatic Ti O2 oxide.The Ti element and Al element in oxide layer presented a complementary trend, and the addition of boron element promoted the densification of oxidation layers and improved the oxidation resistance of Ti-7Al matrix alloy. |
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