Surface Polishing Treatment Research Articles

Dense titanium coatings by modified HVOF spraying

Titanium has an excellent corrosion property in chloride containing environments such as seawater. A modified high velocity oxy-fuel (HVOF) spray process was developed by introducing a mixing chamber between the combustion chamber and the powder feed port. Nitrogen gas was fed into the mixing chamber to control the temperature of the combustion gas generated in the combustion chamber. By controlling the flow rate of nitrogen, various Ti coatings with different degrees of oxidation and porosities could be fabricated. The densest coating produced by this process with surface polishing treatment maintained excellent corrosion protection over a steel substrate in artificial seawater in a laboratory test over 1 month.

Effect of metal alloy surface stresses on the viability of ROS-17/2.8 osteoblastic cells

In this study we compared the effect of structural stresses and surface roughness on biocompatibility of NiTi- and Ti-alloy for ROS-17/2.8 osteoblastic cells. We suggest here that cell viability and cell attachment are linear functions of internal (structural) stress and subgrain size of the implant alloy. However, this is not the case with surface roughness. The two-phase state in these materials is characterized by different mean values of structural stresses ( σ) in α-martensite and β-phase. We found a straight correlation between cell viability and σ β / σ α ratio. Atomic force microscopy revealed that, even after equal surface polishing treatments, roughness varied significantly between the different alloys. The effect of the surface structure of the alloy on the osteoblastic ROS-17/2.8 cell survival rate was studied with combined calcein-ethidium-homodimer fluorescence labeling. The possible effects on cell attachment to substrate were studied by staining the focal contacts with paxillin antibody. All the NiTi surfaces were tolerated well and the cells attached most abundantly to the roughest NiTi surface but the smoothest Ti-alloy surface. However, other parameters of the material state, such as the surface stresses created by hot rolling seem to be responsible for some of the attachment and cell survival features observed in this study.

The effect of heat treatment and surface treatment on the crystallisation behaviour of amorphous Fe 40Ni 40B 20

The effects of various pre-annealing and surface polishing treatments on the crystallisation behaviour of amorphous Fe 40Ni 40B 20 have been investigated by a combination of differential scanning calorimetry, optical and transmission electron microscopy, and X-ray diffractometry. The results show that the crystallisation kinetics are not significantly affected by either pre-annealing or mechanical polishing alone. However, certain combinations of pre-annealing and surface polishing, typically pre-annealing at 350°C for 20 h followed by mechanical polishing with 1200 SiC, change the crystallisation process from bulk nucleation and near-spherical growth to surface nucleation and planar inward growth, with a corresponding sharp increase in the overall crystallisation rate, and a modification in the crystallisation rate law from Y = 1 − exp(− Kt 3) to Y = K' t. For both surface and bulk nucleation crystallisation mechanisms, transmission electron microscopy and X-ray diffractometry show a eutectic crystal structure, consisting of a fine scale lamellar mixture of orthorhombic (Fe, Ni) 3B and f.c.c. (Fe, Ni). The increase in the overall crystallisation rate after pre-annealing and surface polishing is caused by a much higher number of nuclei at the surface compared to the bulk, with little change in the eutectic crystal growth rate. At 390°C, the nucleation density is ≈7 × 10 13 m 3 for bulk nucleation and ≈10 13 m 2 for surface nucleation, while the eutectic crystal growth rate is ≈5 μm/s in both cases. The growth rate constants obey the Arrhenius law over the temperature range 381–396°C with an activation energy of ≈3.0 eV/atom. Surface nucleation of the crystallisation process in amorphous Fe 40Ni 40B 20 can be stimulated either by mechanical deformation of B-rich amorphous particles in the phase-separated, relaxed amorphous alloy structure, or by Ni enrichment at the amorphous alloy surface.