Indian Journal of Engineering & Materials Sciences Vol. 24, October 2017, pp.362-368 Boriding kinetics and mechanical properties of borided commercial-purity nickel A Calik a , N Ucar b *, K Delikanli a , M Carkci a & S. Karakas c a Department of Manufacturing Engineering, Suleyman Demirel University, 32260 Isparta, Turkey b Department of Physics, Suleyman Demirel University, 32260 Isparta, Turkey c Department of Materials Science and Engineering, Çankaya University, 06810 Ankara, Turkey Received 15 February 2016; accepted 17 March 2017 Kinetics of boride layer growth and tensile behaviour in borided commercial-purity nickel was investigated. Boriding was carried out in a solid medium consisting of Ekabor-II powders at 1173, 1223 and 1273 K for periods of 3, 5 and 8 h. Scanning electron microscopy (SEM) and optical microscopy showed column morphology in the boride layer. X-ray diffraction (XRD) analyses indicated that the boride layer formed on the surface consisted mainly of Ni 2 B, with precipitates of Ni 6 Si 2 B. A parabolic relationship between layer thickness and processing temperature was observed. The obtained results showed that although the boride layer thickness increased with increasing boriding temperature and time, boriding parameters had no significant effect on the hardness of the boride layer or the matrix. Tensile properties were negatively influenced by the boriding treatment; both yield and tensile strength values decreased due to the presence of the hard yet brittle surface coating. In addition, the growth kinetics of boride layers was also analysed. The results showed a nearly parabolic relationship between the layer thickness and the process temperature, with activation energy of 47.3 kJ mol -1 . Keywords: Ni, Boriding, Powder pack, Boride layer, Hardness Nickel and nickel-based alloys are widely used in chemical, energy conversion, power production, waste incineration, pharmaceutical and many other industries due to their good corrosion resistance in extreme temperatures and aqueous environments 1-3 . However, pure nickel is not considered for applications where wear resistance is of primary concern 4 . In order to improve its mechanical properties, many surface treatments have been suggested 5,6 . One of these surface treatments is boriding, a thermo-chemical surface hardening treatment in which boron diffuses into the surface of the work-piece to form hard borides with the base material 7-11 . Corresponding to this, it has been shown that the formation of the hard metal borides on the surface provides desirable results in terms of wear resistance 12-14 . Mua et al. 12 studied the effects of boriding time and temperature on the boriding of 99.9% pure nickel. Boriding was performed by means of the powder- pack method using commercial LSB-II powders (containing SiC as a diluent). Boride (Ni 2 B) and silicide (Ni 5 Si 2 , Ni 2 Si) phases were detected on the surface of the borided specimens. They also observed that depending on boriding time and temperature, the thickness of the coating ranged from 36 to 237 µm. The hardness values were 832 HV 0.01 for the silicide layer, 984 HV 0.01 for boride layer, and 139 HV 0.01 for the Ni substrate. The same phases were also observed by Ozbek et al. 15 in borided 99.5% purity nickel, and the microhardness of silicides formed on the surface of the nickel substrate were reported to reach hardness values of up to 805 HV. These two studies indicate that borided metals, owing to their high surface hardness and corrosion resistance, are potential candidate materials for various industrial applications as well as for biomedical applications such as joint arthroplasty. In addition to these studies, in the literature 3,12,16 , comprehensive studies have been attempted to understand the boriding parameter effects on the hardness, boride layer thickness and phases formed boride layer of pure Ni samples. However, current knowledge concerning boride layer growth kinetics on the surface of pure Ni is limited. In the present work, commercial-purity Ni was borided using the powder-pack method and the effect of boriding time on both microhardness and plastic deformation has been studied in detail. Also, growth kinetics such as average activation energy (Q) and growth rate constant (K) for the diffusion of boron in commercial purity Ni were studied by measuring the thickness of the boride layer. ____________ *Corresponding author (E-mail: [email protected])
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Indian Journal of Engineering & Materials Sciences
Vol. 24, October 2017, pp.362-368
Boriding kinetics and mechanical properties of borided commercial-purity nickel
A Calika, N Ucar
b*, K Delikanli
a, M Carkci
a & S. Karakas
c
aDepartment of Manufacturing Engineering, Suleyman Demirel University, 32260 Isparta, Turkey bDepartment of Physics, Suleyman Demirel University, 32260 Isparta, Turkey
cDepartment of Materials Science and Engineering, Çankaya University, 06810 Ankara, Turkey
Received 15 February 2016; accepted 17 March 2017
Kinetics of boride layer growth and tensile behaviour in borided commercial-purity nickel was investigated. Boriding
was carried out in a solid medium consisting of Ekabor-II powders at 1173, 1223 and 1273 K for periods of 3, 5 and 8 h.
Scanning electron microscopy (SEM) and optical microscopy showed column morphology in the boride layer. X-ray
diffraction (XRD) analyses indicated that the boride layer formed on the surface consisted mainly of Ni2B, with precipitates
of Ni6Si2B. A parabolic relationship between layer thickness and processing temperature was observed. The obtained results
showed that although the boride layer thickness increased with increasing boriding temperature and time, boriding
parameters had no significant effect on the hardness of the boride layer or the matrix. Tensile properties were negatively
influenced by the boriding treatment; both yield and tensile strength values decreased due to the presence of the hard yet
brittle surface coating. In addition, the growth kinetics of boride layers was also analysed. The results showed a nearly
parabolic relationship between the layer thickness and the process temperature, with activation energy of 47.3 kJ mol−1.