Hydroxyapatite (HAp Ca 10 (PO 4 ) 6 (OH) 2 ) is very known to be a biomaterial and an absorbent for chromatography. In this study, HAp was agglomerated with anatase TiO 2 to manufacture thermal spray powders to improve the absorption activity of TiO 2 and then improve its photocatalytic activity. The microstructures and compositions of plasma sprayed TiO 2 , TiO 2 -10%HAp, TiO 2 -30%HAp and HAp coatings were investigated. Due to the low thermal conductivity of HAp compound, not all HAp particles fully melted even under the arc current of 800 A. Low temperature stable β-Ca 3 (PO 4 ) 2 was detected in the sprayed HAp coatings. The addition of HAp inhibited the phase transformation of anatase TiO 2 to rutile. Under the arc current of 600 A, the anatase content in the TiO 2 , TiO 2 -10%HAp and TiO 2 -30%HAp coatings was 10.6%, 20% and 42%, respectively. Although slightly decomposition of HAp to α-Ca 3 (PO 4 ) 2 was found in the TiO 2 -30%HAp coatings, it did not decompose to CaO and P 2 O 5 according to the XRD and EDAX analysis. With the increasing of the spraying distance from 70 mm to 110 mm, the anatase content in the TiO 2 -30%HAp coatings decreased from 34% to 17% under arc current of 700 A. The addition of the secondary gas of helium has no significant influence on the melting state of the TiO 2 -HAp feedstock powders.

The compositions and photocatalytic activity of plasma sprayed TiO 2 , TiO 2 -30%FeTiO 3 , TiO 2 -50%FeTiO 3 and FeTiO 3 coatings were investigated. The influence of FeTiO 3 compound on the photocatalytic activity of TiO 2 coating was clarified. The TiO 2 -30%FeTiO 3 coating sprayed under the arc current of 400 A had good photocatalytic activity because the coating did not contain the unfavorable Fe 2 TiO 5 phase. The relative deposition speed of TiO 2 -30%FeTiO 3 powder under the arc current of 400 A was approximate to 4 µm/pass. Although pure FeTiO 3 compound nearly did not show photocatalytic performance, the existence of FeTiO 3 could improve the photocatalytic activity of anatase TiO 2 if FeTiO 3 contacts coherently with it, which was explained using two-steps electron transfer model.

Aluminum alloy has been gradually utilized in cylinder block instead of ferrous casting material for weight reduction in automobile industry these days. In order to acquire more weight reduction, a new liner-less technology - without cast iron liner used - is putting into practice in the fields of aluminum cylinder block and the target is for diesel engine. However, diesel fuel's impurity "sulfur" element and corrosive attack risk, such as sulfuric acid generated to the surface of liner is higher than gasoline fuel. Because of such disadvantage, wear and corrosion resistances applied to the inner cylinder-bore are required in order to achieve this liner-less aluminum cylinder block. This research is intended to accomplish both wear and corrosion performances using plasma thermal spray technology and to verify the feasibility of application to actual engine bore. A newly-developed ferrous powder (Fe-C-Ni-Cr-Cu-V-B alloy) revealed extremely excellent corrosion and wear resistances, compared with currently used bulk casting materials such as Fe-C-Si-B alloy and Fe-C-Si-Mo-B alloy for cylinder liner. For the last time, the new ferrous alloy powder was applied to actual engine bore by using Rota-Plasma spray coating. The experimental results with engine bore presented potential equivalent to current engine bore.

Fatigue properties of the Al 2 O3 plasma-sprayed SUS316L stainless steel rod specimens coated on different spraying conditions have been studied in a physiological saline solution (0.9 % NaCl solution) to evaluate the potential of surgical implant application. Fatigue tests were conducted in push-pull loading at the stress ratio of R = -1, and frequency of 2 Hz. Microstructure related with fatigue damage was examined by SEM and TEM. The fatigue strength of Al 2 O 3 plasma-sprayed metals significantly depended on spraying conditions: the effects of spraying on fatigue strength decreased with increasing the applied stress amplitude. As-blasted specimens were higher in fatigue strength than Al2O3 plasma-sprayed specimens. It was found that the plasma spraying had significant effects on fatigue crack growth behavior in the early stage of crack propagation. Fatigue cracks preferentially originated from dents that had been caused on the substrata metal surface subjected to grit-blasting. These results are discussed with both the compressive residual stresses due to the grit blasting which was carried out prior to plasma spraying and the corrosion-resistance of the alumina deposit.