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UDC 533.9:539.4.015.2
DOI: 10.20310/1810-0198-2016-21-3-850-852
FORMATION OF STRUCTURE AND PHASE COMPOSITION OF Ti-Y SURFACE LAYER BY ELECTRO EXPLOSION AND ELECTRON-BEAM TREATMENT
© V.E. Gromov1), K.V. Sosnin1), Y.F. Ivanov2'3), E.V. Zenina1), Y.A. Rubannikova1)
1) Siberian State Industrial University, Novokuznetsk, Russian Federation, e-mail: [email protected] 2) NR Tomsk Polytechnic University, Tomsk, Russian Federation, e-mail: [email protected] 3) Institute of High-Current Electronics, Siberian Branch RAS, Tomsk, Russian Federation, e-mail: [email protected]
Surface layers containing oxides and carbides of titanium and yttrium are prepared by the electroexplosive doping of titanium with yttrium. The formation of a modified surface layer (enriched in yttrium, carbides and oxides of titanium and yttrium) leads to a threefold increase in the microhardness of the titanium, a more than twofold decrease in the fri c-tion coefficient of the doped layer, and a more than 2.8-fold decrease in the wear rate. Key words: titanium, electroexplosive doping with yttrium, electron irradiation, modified layer.
According to the state diagram, yttrium and titanium are completely miscible in the liquid state; upon solidification, they form a eutectic mixture of two limited solid solutions [1]. In the solid state (below a temperature of 875 °C), the material is a mixture of two (a-Ti and a-Y) phases. The a-Y phase is formed through a reverse peritectic reaction at T = 1440 °C; the eutectics are formed at ~ 20 at % Ti and a temperature of 1355 °C; and the a-Ti phase is formed through a eutectoid reaction at T = 875 °C. Since yttrium and titanium exhibit low solubility in the solid state, the constants of the hexagonal crystal lattices of a-Ti and a-Y vary only slightly upon doping of one metal with the other [1]. Thus, the Ti-Y system belongs to partially miscible binary systems that do not have intermetallic compounds and is of considerable interest for the development of materials with improved properties [2-3]. Alloys based on these systems with a high content of one of the components which deliberately exceeds the limit of its solubility in the other component make it possible to prepare materials with fairly high physical and mechanical characteristics via a relatively simple method [3-4].
Commercially pure titanium VT1-0 was used as the base material [5]. The surface layer of the Ti-Y system was formed according to a two-stage scheme. At the first stage, the electroexplosive doping method was used (EVU-60/10M setup of the Siberian State Industrial University, Novokuznetsk) [6]. A foil of commercially pure titanium VT1-0 with a weight of 100 mg was used as the explosive electroconductive material. A 400-mg weighed portion of yttrium nanopowder was placed on the foil in the region of the explosion. The time of plasma treatment of the sample surface was ~100 ^s; the absorbed power density along the axis of the jet was ~5.5 GW/m2; the pressure in the shock-compressed surface layer was ~12.5 MPa; the residual gas pressure in the chamber was ~100 Pa; the plasma temperature at the nozzle output was ~104 K; the thickness of the surface alloy was ~30 ^m; and the thickness of the heat-affected zone was ~50 ^m. Subsequent high-speed heat treatment of the alloy was conducted with a high-intensity pulsed electron beam using a SOLO system (Institute of
High-Current Electronics, Siberian Branch, Russian Academy of Sciences, Tomsk). Estimates show that, at an electron-beam exposure time for the metal surface of 50200 ^s, the heating and cooling rates for the modified layer are ~106 K/s [7]. In the exposure mode the electron energy was 18 keV; the electron-beam energy density was 20 J/cm2; the pulse duration was 150 ^s; the number of pulses was 3; and the pulse-repetition frequency was 0.3 s-1. Examination of the surface morphology and determination of the elemental and phase composition were conducted by optical microscopy, scanning electron microscopy, and X-ray diffraction analysis.
The electroexplosive doping of the commercially pure titanium surface with titanium and yttrium leads to the formation of a multilayer structure. A coating with a highly developed relief composed of microdroplets, floating metal, micropores, and microcracks is formed on the surface (Fig. 1). Electron-probe microanalysis of this coating revealed the presence of oxygen and carbon atoms in addition to titanium and yttrium; this fact can be attributed to doping of the material under low-vacuum conditions.
The distribution of the detected elements over the surface layer is fairly nonuniform, as evidenced by the analysis results shown in the table. The most nonuniform distribution in the surface volume of the material is found for yttrium; its concentration can differ from region to region by 5-8 times.
Exposure of the sample after electroexplosive doping to a high-intensity electron beam leads to melting of the surface layer. As a consequence, the surface topography becomes smooth and the micropores almost completely disappear; however, the microcracks remain. An island structure is formed on the exposed surface. Electron-probe mi-croanalysis showed that the majority of the surface layer is enriched in yttrium and islands with a size of 10-40 ^m are enriched in titanium.
The islands and regions between them contain globular inclusions with sizes varying in the range 100-300 nm. The former and the latter contain yttrium and titanium inclusions, respectively.
2016. T. 21, Bhm. 3. ®H3HKa
The possibility of the formation of this eutectic at an yttrium concentration of 18 at % has been indicated in [8].
Quite frequently, the interface between the titanium-enriched islands is the place of origin of a plate-like titanium/yttrium eutectic. The transverse sizes of the platelike eutectic elements vary in the range of 200-300 nm.
Electron-probe microanalysis revealed that the yttrium and titanium concentration in the eutectics is 85 and 15 at %, respectively. It should be noted that in the case of equilibrium crystallization of the titanium-yttrium system, the eutectic is formed at 80 at % of yttrium [1].
The high-intensity electron-beam melting of the surface layer of the titanium/yttrium system formed by electroex-plosive doping is accompanied by dispersion of the structure not only of the exposed surface, but also the total volume of doping with a thickness of 30-40 ^m. The most significant modification is undergone by the structure of the surface layer with a thickness of 10-15 ^m, which is apparently formed during crystallization of the layer melted by the electron beam.
The surface modification of titanium by a combined method (exposure to plasma formed during the electrical explosion of a conductive material and subsequent treatment with a high-intensity electron beam) is accompanied by significant improvement in the mechanical and tribolog-ical properties of the material. That is, the microhardness of the 20-^m-thick surface layer increases approximately threefold (compared to the substrate), the friction coefficient of the doped layer decreases more than twofold, and the wear rate decreases more than 2.8-fold.
A surface alloy of the titanium / yttrium system has been formed by electroexplosive doping and electron-beam treatment. The structure, elemental and phase composition, and mechanical and tribological properties of the doped layer have been studied. It has been shown that the elec-troexplosive doping of titanium with yttrium is accompanied by saturation of the surface layer with oxygen and carbon atoms, which leads to the formation of oxides and carbides of titanium and yttrium. Subsequent electron-
beam irradiation is accompanied by dispersion of the structure to a nano- and submicron state and a decrease in the oxygen and carbon concentrations in the surface layer. The formation of two types of eutectics has been revealed. It has been shown that the eutectics enriched in titanium and yttrium have a globular and plate-like shape, respectively. It has been found that the formation of a surface layer enriched in yttrium and oxides and carbides of titanium and yttrium leads to a significant (about threefold) increase in the microhardness of the titanium, a more than twofold decrease in the friction coefficient of the doped layer, and a more than 2.8-fold decrease in the wear rate.
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GRATITUDE: This work was supported by the Russian Foundation for Basic Research (project no. 15-08-03411a and 13-08-98084_r-a-sibir') and the Ministry of Education and Science of the Russian Federation (project no. 2708, project no. 3.1496.2014/K).
Received 10 April 2016
УДК 533.9:539.4.015.2
DOI: 10.20310/1810-0198-2016-21-3-850-852
ФОРМИРОВАНИЕ СТРУКТУРЫ И ФАЗОВОГО СОСТАВА ПОВЕРХНОСТНОГО СЛОЯ Ti-Y ЭЛЕКТРОВЗРЫВНЫМ ЛЕГИРОВАНИЕМ И ЭЛЕКТРОННО-ПУЧКОВОЙ ОБРАБОТКОЙ
© В-E. Громов1), К.В. Соснин1), Ю.Ф. Иванов2,3), Е.В. Зенина1), Ю.А. Рубаннникова1)
^ Сибирский государственный индустриальный университет, г. Новокузнецк, Российская Федерация,
e-mail: [email protected] 2) Национальный исследовательский Томский политехнический университет, г. Томск, Российская Федерация,
e-mail: [email protected]
3) Институт сильноточной электроники СО РАН, г. Томск, Российская Федерация, e-mail: [email protected]
Поверхностные слои, содержащие оксиды и карбиды титана и иттрия получают путем электровзрывного легирования титана с иттрием. Формирование модифицированного поверхностного слоя (обогащенных иттрием, карбидов и оксидов титана и иттрия) приводит к трехкратному увеличению микротвердости титана, более чем двукратному снижению коэффициента трения в легированном слое, и более чем в 2,8 раза снижению износа. Ключевые слова: титан, электровзрывное легирование иттрием электронным облучением модифицированного слоя.
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6. Багаутдинов А.Я., Будовских Е.А., Иванов Ю.Ф., Громов В.Е. Физические принципы электровзрывного легирования металлов и сплавов. Новокузнецк: СибГИУ, 2007.
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8. Gong W.-P, Chen T.-F, LiDa-J, Liu Y. // Trans. Nonferrous Met. Soc. Chin. 2009. V. 19. Р. 199.
БЛАГОДАРНОСТИ: Работа выполнена при поддержке РФФИ (проект N 15-08-03411а и 13-08-98084_р-а-сибирь) и Министерства образования и науки РФ (проект N 3.1496.2014/K).
Поступила в редакцию 10 апреля 2016 г.
Gromov Victor Evgenievich, Siberian State Industrial University, Novokuznetsk, Russian Federation, Doctor of
Physics and Mathematics, Professor, Head of Physics Department named after Professor V.M. Finkel, e-mail: [email protected]
Громов Виктор Евгеньевич, Сибирский государственный индустриальный университет, г. Новокузнецк, Российская Федерация, доктор физико-математических наук, профессор, зав. кафедрой физики им. проф. В.М. Финкеля, e-mail: [email protected]
Sosnin Kirill Valerevich, Siberian State Industrial University, Novokuznetsk, Russian Federation, Post-graduate Student, Physics Department named after Professor V.M. Finkel, e-mail: [email protected]
Соснин Кирилл Валерьевич, Сибирский государственный индустриальный университет, г. Новокузнецк, Российская Федерация, аспирант, кафедра физики им. проф. В.М. Финкеля, e-mail: [email protected]
Ivanov Yuriy Fedorovich, Institute of High Current Electronics Siberian Branch of RAS, Tomsk, Russian Federation, Doctor of Physics and Mathematics, Professor, Main Research Worker, e-mail: [email protected]
Иванов Юрий Федорович, Институт сильноточной электроники СО РАН, г. Томск, Российская Федерация, доктор физико-математических наук, профессор, главный научный сотрудник, e-mail: [email protected]
Zenina Elena Vladimirovna, Siberian State Industrial University, Novokuznetsk, Russian Federation, Student, e-mail: [email protected]
Зенина Елена Владимировна, Сибирский государственный индустриальный университет, г. Новокузнецк, Российская Федерация, студент, e-mail: [email protected]
Rubannnikova Yuliya Andreevna, Siberian State Industrial University, Novokuznetsk, Russian Federation, Student, e-mail: [email protected]
Рубаннникова Юлия Андреевна, Сибирский государственный индустриальный университет, г. Новокузнецк, Российская Федерация, студент, e-mail: [email protected]
