The low cycle fatigue behavior of AA2219-T87 was studied at ambient temperature using fully reversed total strain controlled fatigue tests in longitudinal and transverse orientations. Tension-compression cyclic tests were carried out under total strain amplitude control with strain ratio Rε = −1 and at a frequency of 0.5 Hz. The total strain amplitude was varied from ±0.4 to ±1.5 %. The low cycle fatigue results were analyzed to determine the cyclic stress strain curves. The cyclic strain hardening parameters were evaluated from the cyclic stress–strain curves. Important fatigue parameters namely fatigue ductility coefficient, fatigue ductility exponent, and fatigue strength coefficient were evaluated. The material exhibited cyclic strain softening in both longitudinal and transverse directions. Analysis of the experimental results showed that the stress–strain hysteresis loops exhibited inflections in the first few cycles and the plastic strain amplitude versus fatigue-life plots exhibited bi-linear relationship. The geometry of hysteresis loops and the occurrence of Masing behavior are analyzed and found that the alloy in peak aged condition exhibited tendency towards Masing behavior.
The development of advanced machining techniques requires high-performance tool coatings. To improve the wear resistance and cutting performance of AlTiN coatings, a structure optimization strategy involving bias control and a nano-multilayer architecture strategy is presented. The investigated AlTiN coatings were deposited by cathodic arc evaporation and studied with regard to phase structure, hardness, adhesion, and tribological properties by a combination of X-ray diffraction, nanoindentation, scratch, and ball-on-disk friction tests. A high bias potential (up to −120 V) with enhanced adatom mobility suppressed the formation of the wurtzite structure AlN in AlTiN. In addition, the epitaxial growth of Al0.67Ti0.33N on Al0.5Ti0.5N in the AlTiN nano-multilayer could also promote the single-phase structure. The hardness of AlTiN-based coatings with a dominated cubic structure was 3–4 GPa higher than conventional ones. In addition, the interlayer interfaces in the Al0.67Ti0.33N/Al0.5Ti0.5N multilayer could deflect the cracks and thus improve the fracture toughness. As a consequence, the Al0.67Ti0.33N/Al0.5Ti0.5N multilayer with enhanced mechanical properties obtained the lowest wear rate of 1.1 × 10−5 mm3/N·m and the longest cutting lifetime of 25 min during dry turning the SUS304 stainless steel.
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