Minimisation corrosive attack in the conus-interface of modular endoprothesis by means of definite surface modification via warm deep rolling

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For interfaces between single components of modular endoprotheses the mechanical engineering self-locking morse-taper joint is well established, which is subjected to enormous loadings during physiological application. As material the biocompatible metallic implant material Ti6Al4V with bio inert properties is mainly applied. During the loading micro-movements between the titanium (base) components occur, which might lead to fretting corrosion processes (stress corrosion, fretting corrosion or mechanically induced crevice corrosion) and early failure. Within the scope of the project a warm deep rolling will be carried out by which means beside the process induced work hardening a definite surface topography will be achieved. Additionally, the very surface region of the cone will be softened through a local induction heat treatment, which directly occurs right in advance to the deep rolling process. Subsequently, the softened and structured cone surface can deform plastically during joining of the components (self-accommodation of the joint). As a consequence a local sealing of the joint gap against the penetration of corrosive joint fluid is achieved. Furthermore, local work hardening and stabile compressive residual stresses will be induced. Through the deep rolling treatment corrosion processes in form of ion release, volumetric wear and superficial materials attack at modular interfaces will be reduced. In addition the consecutive local thermal and mechanical treatment further increases the corrosion resistance in contrast to a pure mechanical surface treatment. Objective and task within the scope of the project is to choose (a) the shape of the cone in combination with the parameters for the mechanical surface treatment and (b) the local induction heat treatment such that an optimum result is achieved with regard to fretting fatigue and fretting corrosion. Subsequently, the findings gained in the course of the project allow the implant manufacturer to encounter the still unsolved problem of fretting corrosive wear. Finally, the historically established cone interface can be adjusted to the application needs of modern implant systems. In the end the project aims at the minimization of material and design caused implant failures against the background of reducing the physical and psychological pressure of patients and of the health care system.