Papers by Keyword: Hardness Gradient

Abstract: Thermo-reactive deposition (TRD) salt bath Nb-Cr co-diffusion process was brought forward to prepare the functionally gradient chromium-niobium carbide coating. In TRD salt bath Nb-Cr co-diffusion treatment, T10 steel samples were delved into TRD salt. The samples were treated at 880°C for 3.5 h and then at 950°C for 2.5h. The obtained coatings were characterized by means of microstructure, microhardness, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and X-ray diffraction analysis (XRD). The cross-section hardness of the chromium-niobium carbide coating obtained on the surface of T10 steel samples transits smoothly. The coating was dense, smooth and compact. The thickness ratio of the niobium carbide layer (the outer layer) and the chromium carbide layer (the inner layer) was 4. The hardness of chromium-niobium carbide coating was about 2751HV_0.05, which is between the single chromizing and single niobium. The results showed superior wear properties of the coated samples. The kinetics of chromium-niobium carbide coating was also studied.

Abstract: This paper studied the change of surface hardness after high-cycle fatigue (HCF) test of TC11 alloy with and without Shot Peening (WSP). The results showed that the surface hardness gradient of WSP specimens increased after R=-1 and R=0.1 HCF tests. It was found that the depth and magnitude of surface hardness gradient were related to the stress intensity and cyclic times of HCF, which increased with stress intensity; however, the surface hardness gradient of Shot Peening specimens after HCF maintained the same with that before HCF tests, the values of surface hardness varied slightly after HCF. According to analysis, the surface hardness change of WSP TC11 alloy is related to their surface integrity, which, during the cyclic loading, is due to the higher stress concentration generated on the original machining marks and the cyclic softening of surface layer generated by multi-directional stress.

Abstract: Welding of low carbon martensitic steels with yield strengths above 690 MPa requires careful attention to the welding procedure to avoid hydrogen assisted cold cracking (HACC) and to minimise degradation of the mechanical properties of the weldment. Investigations of the microstructural and hardness gradients in the heat affected zone (HAZ) of these types of steels revealed that the peak hardness does not occur in the grain coarsened heat affected zone (GCHAZ) adjacent to the fusion boundary, as normally observed for ferritic steels, but is displaced towards the grain refined region (GRHAZ). This phenomenon, referred to as the displaced hardness peak (DHP) effect, is considered to arise when the hardenability of the steel is sufficiently high to produce the same microstructure in the both the GC and GR heat affected zones, but the enhanced structural refinement of the GRHAZ increases the hardness and strength above that of the GCHAZ. Implications relative to the susceptibility of the weldments to HACC are discussed.

Abstract: This article describes the flexibility and the potentials of the most important finish for aluminium-based materials. After a suggestion for the classification of anodizing processes, the historical development of the electrolytic anodic oxidation (EAO) and the plasma-electrolytic anodic oxidation (PAO) are presented. In the following section the focus is given on selected topics concerning the process parameters, the microstructure including the layer composition and properties. The variability of the anodizing process parameters and the used materials provide this variety of application. Furthermore, both differences and similarities of the EAO and PAO processes are shown. The conclusion of this review emphasizes that there is still some need for further research especially in the interaction of the process, the formed microstructure and the resulted properties determining the final application. Hence new possibilities for this surface treatment will be open.