Исследование выполнено при финансовой поддержке РФФИ в рамках научного проекта № 16-33-60066 мол_а_дк.
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Surface hardening of Cp-titanium by non-vacuum electron beam cladding of powder mixtures
ARTICLE INFO
Article history:
Received: 28 February 2018 (Дата поступления работы в редакцию. Важно: Работа должна поступить не позже, чем за 3 месяца до официального выхода номера в свет согласно графику. В исключительных случаях, по согласованию с редакцией журнала, срок приема статьи в ближайший номер может быть продлен, но не более чем на две недели.)
Revised: (Дата указывается редакцией)
Accepted: (Дата указывается редакцией)
Available online: (Дата указывается редакцией)
Keywords
Cp-titanium,
Electron beam treatment,
Coating,
Boron carbide,
Titanium carbide,
Titanium boride,
Tribotechnical characteristics.
ABSTRACT
Introduction. Modern engineering copes with different tasks associated with the modification of the structure of the surface layers of metallic materials using high-temperature heating sources. Structural transformations that occur during this treatment make it possible to increase the strength, corrosion and tribological properties of metals. Titanium and its alloys are widely used in modern industry, but its wider distribution is limited by a high coefficient of friction and low resistance to wear. The problem of titanium and its alloys hardening with the use of high-temperature sources of heating is given insufficient attention. Analysis of works related to high-speed heating of titanium-based alloys showed that the laser beam is most often used as a source of surface heating. The
Ti-6Al-4V titanium alloy predominantly performs the function of the base material. The samples obtained by surfacing powder mixtures containing titanium diboride (TiB2) and boron carbide (B4C) possess high hardness and wear resistance. However, the thickness of the coatings formed in this way does not exceed 1 mm. If it is necessary to produce modified layers of increased thickness, it is rational to use the method of electron beam treatment of materials in the air. The aim of the work is to study the possibility of cladding a powder mixture containing boron carbide to modify surface layers of commercially pure titanium by the method of non-vacuum electron beam treatment. Materials and Methods. Cp-titanium is used as the base material. Plates of base material were treated with a highly concentrated electron beam discharged into the air atmosphere. Powder mixtures with different content of boron carbide powder (10, 20 and 30 wt. %) are used to form particles of the high-strength phase in the surface layers. Modified materials are analyzed by optical and scanning electron microscopy. Studies of abrasion resistance are carried out under friction conditions on fixed and loosely fixed abrasive particles. Results and discussion. The mechanical and tribotechnical properties of modified titanium layers are largely determined by structural transformations occurring in the surface layers of the material. The treatment of a titanium alloy with a high-concentration electron beam in the air allows obtaining modified layers with a thickness of more than 1 mm. Cladding of a powder mixture containing boron carbide leads to the formation of high-strength particles in the surface-alloyed layers, which have a significant effect on the properties of the base material. Addition to the cladding mixture 10 wt. % of a boron carbide powder allows to obtain qualitative layers containing finely dispersed particles of titanium monoboride and titanium carbide. The volume fraction of the high-strength phase in these layers is ~ 20%. Increasing the concentration of boron carbide in the original powder mixture to 30 wt. % leads to the formation in the structure of modified layers of large primary crystals of titanium boride and titanium carbide of dendritic morphology. An increase in B4C concentration also leads to an increase in the volume fraction of the strengthening phase to 40- 44%. A characteristic feature of these samples is the presence of conglomerates of fine particles in the lower coverage zone. The average microhardness of the hardened layers reaches 4250-6400 MPa. In the conditions of friction on fixed of abrasive particles, the maximum wear resistance exceeds 2.4 times the same index of the reference sample was recorded during the testing of the alloy obtained by cladding the mixture with 30 wt. % B4C. The same samples showed an eightfold increase in the wear resistance values when the abrasive particles were loosely attached to the material.
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The reported study was funded by RFBR, according to the research project No. 16-33-60066 mol_а_dk.
Conflicts of Interest
The author declare no conflict of interest
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