Showing papers by "U. Kamachi Mudali published in 1995"
TL;DR: In this article, a pit-induced fatigue failure of a stainless steel total hip prosthesis was found to be the cause of failure of the implant, and the study contributed to the understanding of the failure mechanisms of metal fixtures under the action of biomechanical forces.
Abstract: Metals are often chosen as implant materials because of their inherent mechanical properties. Currently the surgical implants are usually made of one of the following three materials: austenitic stainless steels, cobalt-chromium alloys, and titanium and its alloys [1]. Among all of these materials austenitic stainless steels, especially type 316L stainless steels, are widely used because of their relatively low costs and reasonable corrosion resistance [2]. All implant devices are exposed to living cells, tissues and biological fluids which are dynamic and also hostile in nature. Moreover, the design of an implant is dictated by the anatomy and physiology of the skeletal structure of the human body. The artificial mechanical devices are considered to have failed when they are prematurely removed from the body as the implant does not accomplish its intended function, and hence has to be removed due to the implant corrosion and/or fracture. In every failure of an orthopaedic implant the patient is made to experience the trauma of repeated surgery besides severe pain experienced during the process of rejection of the device. The removal of the implant may cause great expense and hardship to the patient. Therefore, it is highly desirable to keep the number of failures to a minimum. Hence, the determination of the mechanism that caused failure of an implant is important, but it is also necessary to explore the event or sequence of events which caused that particular mechanism to become operative. Furthermore, failure investigation will help to improve the total performance of implant devices, besides revealing the details of the mode and origin of the failure mechanism. In spite of the recent innovative metallurgical and technological advances and remarkable progress in the design of implants, failures of implants do occur [3]. Although failures of implants have been reported to be due to fatigue [4, 5], corrosion [6, 7] and/or other general failure mechanisms [8, 9], the underlying causes for the initiation of these failure mechanisms are seldom determined. The causes of failures may also be due to biomechanical reasons rather than to faults in the basic design and/or metallurgy of the implant. The diagnostic study described in this letter reveals that the failure of the implant is typically a pit-induced fatigue failure of a stainless steel total hip prosthesis, and the study contributes to the understanding of the failure mechanisms of metal fixtures under the action of biomechanical forces.
27 citations
TL;DR: Corrosion studies on specimens of nuclear-grade type 304L stainless steel, titanium, Ti-5Ta, and their respective weldments were carried out in a boiling nitric acid medium, as well as in boiling nitrogen acid containing hexavalent chromium and divalent silver ions as discussed by the authors.
Abstract: Corrosion studies on specimens of nuclear-grade type 304L stainless steel, titanium, Ti-5Ta, and their respective weldments were carried out in a boiling nitric acid medium, as well as in boiling nitric acid containing hexavalent chromium and divalent silver ions. The weldments were prepared using a tungsten inert gas welding process. Titanium and its weldment showed excellent corrosion resistance in both media compared to 304L stainless steel. Specimens of Ti-5Ta alloy base showed excellent corrosion resistance, whereas its weldment showed higher corrosion rates in boiling nitric acid medium. Scanning electron microscopy and x-ray diffraction analyses were carried out on the tested specimens to examine the scale morphology and the phases present on the surface.
21 citations
TL;DR: In this article, the authors used a Nd-YAG laser of 300 W power and 9 ms pulse width at a traverse speed of 2.5 mm s−l for melting 304 and 316 stainless steels.
Abstract: Sensitised types 304 and 316 stainless steels were laser surface melted using a Nd–YAG laser of 300 W power and 9 ms pulse width at a traverse speed of 2.5 mm s–l. Pulse energy, pulse repetition rate, and gas atmosphere were varied to give 24 different laser melting conditions. The melted specimens were tested according to ASTM A262 practice A (electrolytic etch test), and ASTM A262 practice E (immersion for 24 h in boiling Cu–CuS04 solution followed by a Ubend test) in order to assess the intergranular corrosion (IGC) resistance. The micro hardness values across the unmelted/melted region were measured and impact tests, with sensitised subsize specimens laser surface melted at the notch, were carried out. The results indicate that on lasersurface melting the sensitised microstructure disappeared and also that the specimens possessed higher IGC resistance. This is attributed to the creation of a desensitised microstructure of 200 μm thickness with dendritic–cellular structure and a heat affected z...
16 citations
7 citations