Abstract
Modification of the surface of VK10KS solid alloy with titanium alongside with boron by the method of pulse-plasma exposure (electro-explosive alloying) is considered. In this case, a superhard (27,500 MPa nanohardness) layer is formed with a thickness of 2.0 – 2.5 μm and a low (μ = 0.10) friction coefficient compared to the friction coefficient of a hard alloy in the sintered state (μ = 0.41). This layer consists of finely dispersed high-hard phases TiB2, (Ti, W)C, W2C (according to scanning, transmission electron microscopy and X-ray phase analysis). Below is a hardened (with a nanohardness of 17,000 MPa) surface layer (heat affected zone) 10 – 15 μm thick, identified by W2C and WC carbides and alloyed with a cobalt binder. This layer smoothly passes into the base. By profilometric studies it was established that after electroexplosive alloying with titanium and boron, the roughness increases (Ra = 2.00 μm) compared to the initial one (Ra = 1.32 μm), but remains within the specifications (Ra = 2.50 μm). The authors have revealed changes that occur in the surface carbide and near-surface cobalt phases during electroexplosive alloying. In the carbide phase, accumulations of dislocations were indicated. In the cobalt binder, deformation bands (slip bands), single dislocations, and also finely dispersed tungsten carbide precipitates were found. This change can be explained by stabilization of the cubic modification of cobalt, the crystal lattice of which has a large number of slip planes during deformation and a greater ability to harden compared to the hexagonal modification of cobalt. Additional alloying with a cobalt binder will positively affect the operational stability of tungsten carbide alloys as a whole due to their stabilization.
Highlights
A superhard (27,500 MPa nanohardness) layer is formed with a thickness of 2.0 – 2.5 μm and a low (μ = 0.10) friction coefficient compared to the friction coefficient of a hard alloy in the sintered state (μ = 0.41)
By profilometric studies it was established that after electroexplosive alloying with titanium and boron, the roughness increases (Ra = 2.00 μm) compared to the initial one (Ra = 1.32 μm), but remains within the specifications (Ra = 2.50 μm)
Yaresko S.I. The influence of the composition of cobalt phase of hard alloys on tool wear upon laser hardening // Russian Journal of Non-Ferrous Metals
Summary
Рассмотрено модифицирование поверхности твердого сплава ВК10КС титаном совместно с бором способом импульсно-плазменного воздействия (электровзрывного легирования). При этом формируется сверхтвердый (нанотвердость 27 500 МПа) слой толщиной 2,0 – 2,5 мкм с низким (μ = 0,10) коэффициентом трения по сравнению с коэффициентом трения твердого сплава в спеченном состоянии (μ = 0,41). Ниже располагается упрочненный (с нанотвердостью 17 000 МПа) приповерхностный слой (зона термического влияния) толщиной 10 – 15 мкм, идентифицированный карбидами W2C и WC и легированный кобальтовой связующей. Исследованиями выявлены изменения, возникающие в поверхностной карбидной и приповерхностной кобальтовой фазах при электровзрывном легировании. В кобальтовой связующей выявлены деформационные полосы (полосы скольжения), единичные дислокации, а также мелкодисперсные выделения карбидов вольфрама). Дополнительное легирование кобальтовой связующей положительно повлияет на эксплуатацион ную стойкость карбидовольфрамовых твердых сплавов в целом из-за своей стабилизации. Сплавы WC – Co – наиболее прочные из известных твердых сплавов. Целью настоящей работы явилось получение упрочненного слоя на поверхности сплава ВК10КС способом электровзрывного легирования с использованием титана и бора, исследование его структуры и свойств
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