Martín Ortiz Domínguez

Characterization and wear performance of boride phases over tool steel substrates

This research work was conducted to characterize boride phases, obtained from the powder-pack process, on AISI H13 and D2 steel substrates, and investigate their tribological behavior. The boriding was developed at a temperature of 1273 K with an exposure time of 8 h. X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were conducted on the borided material to characterize the presence of the FeB, Fe2B, and CrB phases and the distribution of heavy elements on the surface of the substrates. The adherence of the boride layers was evaluated, in a qualitative form, through the Daimler-Benz Rockwell-C indentation technique. Sliding wear tests were then performed using a reciprocating wear test machine. All tests were conducted in dry conditions at room temperature. A frequency of 10 Hz and 15-mm sliding distance were used. The applied Hertzian pressure was 2.01 GPa. Scanning electron microscopy was used to observe and analyze the wear mechanisms. Additionally, the variation of the friction coefficient versus the number of cycles was obtained. Experimental results showed that the characteristic wear mechanism for the borided surface was plastic deformation and mild abrasive wear; for unborided substrates, cracking and spalling were observed.

La mecánica del hueso. Una revisión de los modelos de remodelación óseo

The bone as biological structure is continually adapting to changes in their physical environment, it has been widely accepted that bone respond to mechanical stimulation, tissue is resorbed in regions exposed to low mechanical stimulus, whereas new bone is deposited where the stimulus is high. This process of adaptation is thought to enable bone to perform its mechanical functions with a minimum of mass. From this idea, many theoretical models for bone remodeling use this concept as part of the strategy to simulate bone structural adaptation. What implies the existence of an equilibrium state where the bone structure is adapted to the environment. That is the origin to develop of computational models were, on one hand, the assumption of isotropy of the trabecular structure is made. The results show the similarities in density distribution with in vivo bone, as well as a convergent solution cannot be obtained. To another part, models have been developed to consider the anisotropic nature of the trabecular bone in the continuum level making use of optimization principles; however, despite of some mechanical aspects reflected by these idealized microstructures, they just represent a mathematical abstraction of the trabecular architecture. The aim of this work is to show the models of bone adaptation that employ a mathematical approach to characterize the mechanical properties of the bone structure. Keyworks: Bone, stimuli, bone remodeling, strain energy density