M.A.L. Hernandez-Rodriguez

Failure analysis of a total hip prosthesis implanted in active patient

This work presents an analysis of a total hip prosthesis that failed in service prematurely within 5 years. The prosthesis presented a fractured stem that was extracted from a 46 year old male patient, 75 kg weight and 1.76 m height. In order to determine the origin of the failure, the femoral stem component was analyzed by means of visual inspection; optical microscope (OM), scanning electronic microscopy (SEM) and energy disperse spectroscopy (EDS). The investigation showed that the crack had originated due to a high stress concentration on the anterolateral corner section of the stem. Any discontinuity or defect on the prosthesis surface in this location acted as preferential site to nucleate a crack which propagated by fatigue until the cross section was not able to sustain an eventual high load produced for the active patient.

Optimization of the Severe Plastic Deformation Processes for the Grain Refinement of Al6060 Alloy Using 3D FEM Analysis

An analysis in 3D by means of the finite element method was carried out to study three processes for producing bulk fine-grained materials: dual equal channel angular pressing (DECAP), equal channel angular pressing, and multi-axial forging. For this purpose, a commercial Al6060 alloy in solution heat treatment conditions was utilized. The effect of different values of the coefficients of friction (μ), the plastic flow, the strain hardening behavior, and the effective strain were analyzed. The results obtained from the simulation are in good agreement with the experimental studies. The results indicate that the DECAP process improves the plastic flow and promotes homogeneous strain distribution and grain refinement due to an increase in components of the shear deformation, back-pressure effect, and the diminution of the coefficient of friction.

Microstructure and Mechanical Properties of a Tempered High Cr Martensitic Steel

Microstructural and mechanical studies have been performed in a high Cr martensitic steel Firth-Vickers (FV535) to analyze the tempering of martensite. Nanoindentation technique was used to determine the hardness and elastic modulus through systematic measurements on martensite and tempered martensite. On the other hand, microscopic studies were carried out to analyze the material in the same condition as received and subsequently observe the microstructural modifications after heat treatment. The precipitation presented in the last stage of tempering was observed by transmission electron microscopy. The results showed the effect of the martensite decomposition on the mechanical and nanomechanical properties of FV535.

Micro-Abrasive Wear Testing of Surface Engineered Surgical Grade CoCrMo Alloy for Biotribological Applications

Wear of metal-on-metal hip joints is a concern due to the toxicity and biological reaction of wear debris. Retrieved CoCrMo hip implants have shown that abrasive wear is the predominant failure mechanism in such joints. There have been some efforts to improve the wear resistance of joint implants through the application of hard biocompatible ceramic coatings. However, the adhesion of the coatings has been a concern. The aim of the present work was to study the wear resistance of surface engineered CoCrMo alloy intended for biotribological applications by means of an abrasive wear test, based on the ball-crater technique. Different surface conditions were obtained on surgical grade wrought CoCrMo alloy: plasma nitrided, physical vapor deposition (PVD) coated (monolayer CrN and multilayer (TiN/CrN)×3) and modified using duplex surface engineering technology (a combination of the two previous approaches: plasma nitriding followed by plasma assisted PVD). The engineered surfaces were characterized by scanning electron microscopy, nanoindentation and, atomic force microscopy (AFM). Scratch test was used to determine the influence of the duplex technology on the adhesion of the coatings to substrate. The wear resistance of the different surface conditions was determined using a slurry abrasive micro-abrasion testing device. It was found that the duplex engineering technology enables a significant rise in the resistance of surfaces against concentrated loading modes, improving the adhesion of the coatings to the substrate; however, it has no significant influence improving the wear resistance of the samples during the abrasive wear tests.

Study of Decomposition of Martensite in FV535 Steel

The decomposition of martensite and precipitation presented during this process in the FV535 high-chromium martensitic steel and the effect on mechanical properties were studied. FV535 steel is used in petrochemical plants, gas turbine engineering, aircraft, and aerospace industries. The decomposition of martensite has been divided in six different stages, occurring at different temperature ranges, which can vary depending on the steel composition and microstructure; these stages were analyzed by DSC, and in order to analyze the change in mechanical properties, the FV535 steel was characterized by microhardness tests. The precipitation phenomena that occurred in this type of steel were analyzed by DSC and transmission electron microscopy and were correlated with the change in mechanical properties at high temperatures.