Tatsuhiro Jibiki

On Improvement of Wear Resistant Properties of DLC Film Coated on Cr-Mo Steel in Seawater

海洋資源の利活用は今後ますます発展してくるもの と考えられ,それに伴い資源探査機器・構造物等の性 能や信頼性が重要となっている.これらには多くの摩 擦部分や微小すべりを伴う接触部分があり,その摩 擦・摩耗や腐食に対する技術的課題の解決が急務であ る. 海洋環境で使用できる摩擦材に必要とされる条件は, 耐食性,低摩擦,耐摩耗性がまず挙げられるが,これ らを海洋環境の汚染なく満足する摩擦材は,強度・耐 久性にやや難がある高分子材料等を除けばほとんどな く,またこの分野の研究自体きわめて少ないのが現状 である.これらを踏まえ,本研究は,強度の高い金属 に耐食・低摩擦・耐摩耗性を付与するための表面処理 技術に関する基礎研究の一環として,高硬度,化学的 に安定かつ相手攻撃性の小さい性質をもつDLC膜に注 目し,海水中におけるDLC膜の耐摩耗性の改善を図る ことを目的とした. 周知のように,DLC 膜は工業的にも使われている硬 質薄膜であるが,海水中で用いようとするとき,次の ような考慮あるいは克服すべき点がある.一般に,DLC 膜にはピンホールが存在し,そこから海水が浸入して 基材が腐食することによりDLC膜を破損する可能性, また,たとえピンホールが存在しなくとも摩擦過程で DLC 膜にクラックなどの損傷が発生し,そこから海水 が浸入することにより同様な現象が起こる可能性があ る.そのため,海水中で用いられるDLC膜には耐食性 の高い下地(基材)を用いるか,あるいは何らかの方 法で基材の耐食性を向上させることが必要である. 本研究は,後者の方法の1つとして,カソード防食 技術を応用してDLC膜を有する摩擦材の耐食・耐摩耗 性を向上させようとする試みを行ったものである.す なわち,基材としてクロムモリブデン鋼を用い,そこ にDLC膜を付与したのち,基材よりイオン化傾向の高 い亜鉛(Zn)を被覆してカソード防食を行うことによ り,DLC 膜の欠陥を許容した耐食・耐摩耗性のある摩 擦材を開発しようとする. 以下,試験片(Zn 被覆の方法等),海水浸漬試験, 耐摩耗性評価試験(往復動およびフレッチング試験) の結果について報告する.

Development of Piston-Ring for Marine Diesel Engine. Actual Engine Test Result of Piston-Ring Made from Wear Resisting Steel.

In one direction of improving the material strength of a piston-ring of a marine diesel engine, a new wear resisting steel has been made efforts to develop in the expectation that it may supersede high phosphorus gray cast iron. For the newly developed wear resisting steel (later, wear resisting steel) we carried out wear tests and scuffing tests, and analyzed its test results in comparison with those of gray cast iron. After that we manufactured piston-rings using wear resisting steel. Piston rings made from wear resisting steel were installed the actual engine, and the actual engine test was carried out for 160.8 hours. We inspected the sliding surfaces of piston-rings after 29 hours and 160.8 hours. According to the test results, the wear amount of wear resisting steel was the same or smaller than that of gray cast iron, and the sliding surfaces of piston rings were normal and no severe wear such as scuffing was observed on them.

Improvement of Initial Break-in Condition of Spray Coated Ceramics for Marine Diesel Engine

To avoid separation or abnormal wear of the spray coated ceramics caused by the partial contacting of the initial sliding, it is necessary to improve the initial surface break-in condition of the wear resistant spray coated ceramics of the piston ring and the cylinder linear of the marine diesel engine. The partial contacting wear test of spray coated ceramics was carried out by using pin-on-disk type wear testing machine. The test results of spray coated ceramics with no treatment were compared with that of Ni-P + PTFE plated spray coated ceramics. An observation of wear surface was carried out using together some methods of observation in order to analyze the wear surface in initial break-in condition quantitatively. The main results are in the following: Spray coated ceramics was worn abnormally after partial contacting wear test, but Ni-P + PTFE plated spray coated ceramics was worn normally, protecting from the damage by partial contacting. Phenomenon of surface break-in condition can be evaluated quantitatively by statistical processing of wear surface profile.

Development of Piston-Ring for Marine Diesel Engine

The development of new anti-wear steels instead of gray cast iron has been carried out as one measure strengthening the piston-ring. Using the anti-wear steel, wear test and scuffing test were carried out. The test results of the anti-wear steel were compered wtih that of gray cast iron.The main results are in the following: Wear amount of the anti-wear steel was lower than that of gray cast iron. The anti-wear steel had relatively large variations of scuffing test results. It was necessary for the anti-wear steel with surface modification, as the initial surface break in condition of the steel was not always sufficient. If the initial surface break in condition of the anti-wear steel is improved by surface modifications, the good surface running condition will be achieved without scuffing damage.