Abstract: A sliding spline shaft device of the present invention includes a male spline and a female spline that is fitted to the male spline in an axially slidable manner, and at least one of the splines has a surface processed layer. The surface processed layer includes an undercoat layer, an intermediate layer containing phosphate, and a topcoat layer containing solid lubricant, in this order. The undercoat layer contains iron nitride and/or iron carbide. Thus, the surface of a base material has high hardness. As a result, microscopic deformation of the sliding surface is reduced, and increase in a real contact area is suppressed, whereby stick-slip is prevented.

Abstract: A sliding spline shaft device of the present invention includes a male spline and a female spline that is fitted to the male spline in an axially slidable manner, and at least one of the splines has a surface processed layer. The surface processed layer includes an undercoat layer, an intermediate layer containing phosphate, and a topcoat layer containing solid lubricant, in this order. The undercoat layer contains iron nitride and/or iron carbide. Thus, the surface of a base material has high hardness. As a result, microscopic deformation of the sliding surface is reduced, and increase in a real contact area is suppressed, whereby stick-slip is prevented.

Abstract: A sintered copper alloy material product is provided on which a skin (particularly, a skin of a solid lubricant with low adhesion, such as PTFE or molybdenum disulfide) is securely formed on the surface thereof and has good sliding properties and good seizure resistance under unlubricating environments or under corrosive environments. A sintered copper alloy material is processed using a selective chemical etching solution containing a compound of one kind or more selected from the group of consisting of peroxide, peroxocompound, chromic acid and permanganic acid and a compound of one kind or more selected from the group of consisting of phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, zirconic hydrofluoric acid, titanic hydrofluoric acid, titanic acid, molybdic acid, tungstic acid, vanadic acid, niobic acid, and organic chelating agent. Thereafter, a lubricating skin is on the surface of the processed material.