کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
5349905 1503548 2017 24 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
The influence of the phosphorous content and heat treatment on the nano-micro-structure, thickness and micro-hardness of electroless Ni-P coatings on steel
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی تئوریک و عملی
پیش نمایش صفحه اول مقاله
The influence of the phosphorous content and heat treatment on the nano-micro-structure, thickness and micro-hardness of electroless Ni-P coatings on steel
چکیده انگلیسی
Electroless Ni-P coatings were obtained on steel substrates using different bath compositions, which lead to different phosphorous contents of the coatings. In this paper the effect of the P-content in the Ni-P coatings was experimentally studied on the thickness of the coating, on its nano-micro-structure and on its micro-hardness. The as-received samples were nano-crystalline (mostly amorphous according to XRD) and their micro-hardness was found to decrease with increasing the P-content. Upon annealing at 400 °C a new Ni3P phase was formed and the nano-cystalline Ni-rich grains coarsened to micro-grains. In this annealed state the micro-hardness was found to increase with increasing the P-content. A complex model was built to explain the experimental results. It was supposed that the as-received Ni-P coating contains almost pure Ni nano-grains surrounded by segregated P atoms; as the grain grows, its surface is covered more and more by the P atoms. When the grain is fully covered by the P atoms, further grain growth is inhibited and the coating can grow further only due to nucleation of a new grain. Thus, the size of the grains was found inversely proportional to the P-content of the Ni-P alloy. The need for a larger number of nucleation events with decreasing grain size explains why the coating has a smaller thickness for smaller grain size, i.e. higher P-content. The inverse Hall-Petch rule was found for the grain size dependence of micro-hardness of the as deposited samples due to the grain boundary sliding of relatively hard Ni-rich nano-crystals along the soft P atoms (higher P-content lead to lower micro-hardness through smaller grain size). After annealing the micro-hardness was found to increase with the volumetric phase fraction of the harder Ni3P phase within a relatively soft Ni matrix, i.e. it was found to increase with the P-content of the Ni-P coating. The extrapolated value for the micro-hardness of the Ni3P phase is found about 757 ± 20 HV0.01.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Applied Surface Science - Volume 423, 30 November 2017, Pages 160-169
نویسندگان
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