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Contact Mechauical Properties of Diffusion and Deposition Duplex Modified Layer on Metal Surface

Author: MaYong
Tutor: TangBin
School: Taiyuan University of Technology
Course: Materials Science and Engineering
Keywords: Diffusion and deposition duplex modified layer (DDDML) Micro/nanoindentation Forward analysis Inverse analysis Impact test
CLC: TG174.4
Type: PhD thesis
Year: 2013
Downloads: 37
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Abstract

A diffusion and deposition duplex modified layer (DDDML) with high hardness and high resistance of wear and corrosion can be obtained by using the plasma surface alloying technique after selecting reasonable diffusion elements. DDDML contains a homogeneous deposition layer and a gradient diffusion layer. Compared to homogeneous films, DDDML belongs to metallurgical bonding and its diffusion part can coordinate the deformation between the deposition layer and the substrate. Because the diffusion layer is not only gradient in composition but in elasto-plastic properties, it is difficult to quantificationally determine its mechanical properties. Based on nano/microindentation, low energy repeat impact test and finite element simulation, this paper seeks to determine the elasto-plastic properties of DDDML and investigate its deformation and failure behavior corresponding static and dynamic contact conditions.The research results could provide theoretical references for the design and application of DDDML.Considering that forward analysis is the basis of this paper, it was firstly launched corresponding nanoindentation tests on Ti/SS and Cr/SS systems. Then, based on forward analysis, representative stress and representative strain, this paper sought to present inverse analysis approaches to determine the plastic properties of DDDML. Finally, nanoindentation, microindentation and low energy impact tests were performed. What is more, inverse analysis corresponding nanoindentation test and forward analysis correspongding microindentation and low energy impact tests were lauched. The main results are as follows:(1) According to the forward analysis corresponding nanoindentation tests on the Ti/SS and Ti/SS systems, it can be founded that the elastic modulus is more sensitive than the hardness and the10%rule is not universally true. In the nanoindentation process of soft film/hard substrate system,"pile up" presented, which made the hoop tensile stress exist in the direction perpendicular to the pyramidal edge. Therefore, along the pyramidal edge direction, radial cracks are easy to produce. For the hard film/soft substrate system,"sink in" exhibited in the nanoindentation process, which caused radial tensile stress around the contact circle between the indenter and the sample. Thus ring cracks are easy to form in this area.(2) Based on forward analysis, representative stress and representative strain, two inverse analysis approaches were built (Ⅰ and Ⅱ). The main differences between them are the representative strain of the inverse analysis approach II is of plastic strain and the strain hardening exponent of the inverse analysis approach II was not obtained by a dimensionless function but by repeated simulation modifications.(3) Nanoindentation tests were performed on the cross section and surface of the Mo modified layer. For the purpose of comparison, nanoindentation tests were also performed on the treated and untreated Ti substrates. With the consideration of size effects, the plastic properties of every sub-layer of the Mo modified layer were obtained. Experimental and inverse analysis results indicate that the whole Mo modified layer possesses higher hardness, elastic modulus and retains relatively fine plasticity. Through comparing nanoindentation test results of the treated and untreated Ti substrates, it is concluded that the alloying treatment temperature of900℃has no effect on the mechanical properties of the Ti substrate.(4) Microindentation tests were performed on the surface of the Mo modified layer using the CSM Micro-Hardness Tester (CSM Instruments, Switzerland) with a Vickers diamond tip. Two loading types were adopted, i.e. the linear loading type with three different maximum loads of5N, ION and15N, and the continuous multi-cycle (CMC) loading type with the maximum load of5N reached by30cycles. Linear loading test results indicate that the Mo modified Ti has the same failure mode as the hard film/soft substrate system. CMC loading test results could link with the nanonindentation results. According to the experimental and forward analysis results, the occurrence rule of the ring cracks was concluded. With the increase of the applied load, cracks become bigger and bigger under the indenter. When the load reaches the maximum value, the biggest crack appears around the contact circle. Owing to the expanding of the radial tensile stress, ring cracks continue to propagate at the periphery of the contact circle, but become weaker and weaker.(5) On the surface of the Mo modified layer, low energy impact tests were conducted at four loads of100N,300N,500N and700N with10000impact cycles. The failure process was obtained. Firstly, ring cracks occurred around the contact circle between the impact ball and the sample due to the large plastic deformation. Secondly, radial cracks perpendicular to the ring cracks presented because of impact fatigue. Finally, cohesion failure occurs near the contact circle. During the failure process, there existed the impact wear, especially under the higher impact load. According to the experimental and forward analysis results, the failure model under the ideal impact condition and the higher impact load was established.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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