• A A Ahmad

      Articles written in Bulletin of Materials Science

    • Adhesive B-doped DLC films on biomedical alloys used for bone fixation

      A A Ahmad A M Alsaad

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      The long-term failure of the total hip and knee prostheses is attributed to the production of wear particles at the articulating interface between the metals, ceramics and polymers used for surgical implants and bone-fixtures. Therefore, finding an adhesive and inert coating material that has low frictional coefficient should dramatically reduce the production of wear particles and hence, prolong the life time of the surgical implants. The novel properties of the non-toxic diamond-like carbon (DLC) coatings have proven to be excellent candidates for biomedical applications. However, they have poor adhesion strength to the alloys and biomaterials. The addition of a thin interfacial layer such as Si, Ti, TiN, Mo and Cu/Cr and/or adding additives such as Si, F, N, O, W, V, Co, Mo, Ti or their combinations to the DLC films has been found to increase the adhesion strength substantially. In our study, grade 316L stainless steel and grade 5 titanium alloy (Ti–6Al–4V) were used as biomaterial substrates. They were coated with DLC films containing boron additives at various levels using various Si interfacial layer thicknesses. The best film adhesion was achieved at 8% and 20% on DLC coated Ti–6Al–4V and grade 316L substrates, respectively. It has been demonstrated that doping the DLC with boron increases their adhesion strength to both substrates even without silicon interfacial layer and increases it substantially with optimum silicon layer thickness. The adhesion strength is also correlated with the hydrogen contents in the B-DLC films. It is found to reach its maximum value of 700 kg/cm2 and 390 kg/cm2 at 2/7 and 3/6 for CH4/Ar partial pressures (in mTorr ratio) for Ti–6Al–4V and 316L substrates, respectively.

    • Structural phase transitions and piezoelectric anomalies in ordered Sc0.5Ga0.5N alloys

      A M Alsaad A A Ahmad

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      Local-density approximation calculations (LDA) within density functional theory (DFT) and Berry phase approach within modern theory of polarization are performed to predict the structural and piezoelectric properties of ordered Sc0.5Ga0.5N alloys under compressive and tensile in-plane strain. This alloy is found to exhibit a tremendous piezoelectric response, associated with a phase transition from nonpolar 𝑝63/𝑚𝑐𝑐(𝐷6h) space group to a polar 𝑝63𝑚𝑐(𝐶6v) structure, at fixed Ga and Sc compositions when continuously changing the experimental accessible parameters (i.e. the compressive and tensile strain). The mechanism of the effects behind such anomalous behaviour is revealed and explained.

© 2017 Indian Academy of Sciences, Bengaluru.