11種の純金属Ni, Fe, Pt, Mo, W, Cn, Ag, Al Zn, SnおよびPbの空気中と真空中(10^<-6>mm Hg)における摩擦摩耗を実験的に研究した結果,固体の乾燥摩耗現象が雰囲気の潤滑作用のもとにあることを見いだした.金属の乾燥摩耗形態は,雰囲気により有効な潤滑作用をうけるか否かによって,非付着摩耗と付着摩耗の二つの類形に分類できる.付着域は実験した非遷移金属の全条件下,および遷移金属のすべり速度または見かけ接触圧力pの高い領域であって,vやpの増大に伴なって摩粍率w_sは増大する.そしてすべり距離の少ないあいだはw_sが小さいがある距離をすべると大きくなる.また摩耗面やその内部結晶組織は著しい損傷をうけ,摩擦抵抗の変動ははなはだしく,摩耗粉の外観は金属様で真実接触点1個の大きさに比してはるかに大きい.一方非付着域は遷移金属のp,vの低い領域に存在し,w_sはpやvの減少にともなって増大し,すべり距離にかかわらず一定である.このとき摩耗面やその内部結晶組織は損傷が少なく,摩擦の変動も小,摩耗粉は真実接触点1個の面積に比してはるかに小さい.両域の転移点は雰囲気が稀薄になるに従ってpvの小さい側に移行する.上の事実を説明するため,真実接触面において作られている微小結合部がすべりによって破断されてからその点がふたたび結合を形成するまでの平均自由時間という概念を導入した.この時間内にせん断部に気体分子が十分に衝突吸着することにより化学吸着層(単分子層)を形成する条件が非付着域から付着域に転移する臨界点を決定するという考え方から,Ni/Niについての実験結果を定量的に説明することを試みた.この平均自由時間がpvに逆比例するという計算結果を導き,これを用いて従来知られ,本実験でも再確認した事実-摩耗量のp特性とv特性との機構上の同一性-を合理的に説明することができた.

The nature of adhesive wear of various pure metals such as Ni, Fe, Pt, Mo, W, Cu, Ag, Al, Zn, Sn and Pb including transition and non-transition metals were studied in air under pressure from 760 torr. to 10^<-6> torr. To examine the contributions of surrounding atmosphere to metallic wear, friction and wear were measured by spring type friction apparatus in closed bell-jar in which the stmosphere could be controlled. The test specimens were consisted of a slider with spherical tip and a circular plate. From the vast data of friction, rate of wear and wear particle size for various running conditions and surrounding atmospheric pressures, the nature of adhesive wear in gaseous atmosphere was devided into two types. The one is the non-cohesive and the other the cohesive wear. In general, the non-cohesive wear occured when the rubbing surfaces were lubricated by gas molecules sufficiently and the cohesive wear when not lubricated or not sufficiently lubricated. For non-transition metal combinations, the nature of wear appeared always as cohesive irrespective of running conditions such as loads or rubbing speeds. For transition metal combinations, on the other, cohesive wear appeared only for running conditions of high speeds or heavy loads, and non-cohesive wear for low speeds and light loads. In cohesive wear, for all metals, rate of wear w_s (mm^3/mm) increased with increasing speed v (mm/s) and with increasing apparent mean pressure p (load/apparent contact area, kg/mm^2), but relatively slowly in the early stage of sliding and faster in the later stage. In this cohesive range, the wear track and the grain structure beneath the track were found to be heavily distorted; the friction measured by oscillographic records fluctuated violently during sliding. But the most interesting feature in cohesive range when compared with non-cohesive wear was that the wear particles were always found to be much larger and the rate of wear, on the contrary, much smaller than in non-cohesive range. The wear particle size was found in this range to be much larger than that estimated from the real contact point size. In non-cohesive range which appeared only for transition metals at light loads and low speeds, the rate of wear increased with decreasing speed or with decreasing apparent mean pressure, being nearly constant independent of sliding distances. The wear track and the grain structure beneath the track were found to be less distorted and the fluctuation of friction also was smaller. The wear particles in this range, as described above, were finer than those in cohesive range, being smaller than those estimated from the real contact point sizes. The critical transition point from non-cohesive to cohesive range moved to the lower value of v or p when the surrounding gas pressure was lowered. To explain these experimental results, the authors introduced a concept of mean free time of a small contact point for adsorbing molecules of surrounding gases. When a bridge formed between two contact points was sheared off and a clean small surface was exposed to surrounding gases, it must have a time t until it formed the next bridge when sliding. During this time t, the mean free time of adsorption, the gas molecules could attack the clean spot and could easily form a chemisorped monolayer when the mean pressure p was low (the mean distance between the two neighbouring contact points was small) or when the sliding speed was low. When p or v was high, the mean free time t became too short to adsorb enough molecules for making a monolayer. From a simple theoretical calculation, the time t was deduced as to be inversely proportional to pv. By analyzing the experimental data for Ni on Ni combination, the authors could verify the fundamental relation between the mean free time of adsorption and the value pv, and found that the critical transition point from non-cohesive to cohesive range corresponded to the condition where the mean free time of adsorption was just enough for contact points to form a chemisorbed monolayer of surrounding gases.

資料番号: SA4135106000