Internal friction and its thermal evolution on 304 L stainless steel films

Internal friction has been measured between 300 and 760K on 304 L stainless steel (SS) using a vibrating reed device. The 0.6 µm thick samples were deposited with ion beam sputtering technique on (100) silicon substrate. It has been shown that the damping level is considerably reduced by annealing between 500 and 760K. The calculated activation energy and the reaction order, using the Johnson-Mehl-Avrami (J-M-H) kinetic enable us to assume that the observed mechanism is closely related to microstructural rearrangements located at grain boundaries.Internal friction has been measured between 300 and 760K on 304 L stainless steel (SS) using a vibrating reed device. The 0.6 µm thick samples were deposited with ion beam sputtering technique on (100) silicon substrate. It has been shown that the damping level is considerably reduced by annealing between 500 and 760K. The calculated activation energy and the reaction order, using the Johnson-Mehl-Avrami (J-M-H) kinetic enable us to assume that the observed mechanism is closely related to microstructural rearrangements located at grain boundaries

Characterization of defects in a martensitic CuAlNi shape-memory alloy

A water-quenched martensitic CuAlNi shape-memory alloy was investigated by a combination of coincidence Doppler broadening and positron-lifetime spectroscopy, supported by positron-lifetime calculations. We find a high defect concentration in the as-quenched samples. The positron-lifetime calculations suggest that the defects are not only single vacancies but also vacancies associated with dislocations and stacking faults. Annealing in the martensitic phase has no significant influence on the vacancy concentration but results in a different chemical environment around the vacancies. After aging in the austenitic phase the vacancy concentration decreases significantl

Action observation combined with conventional training improves the rugby lineout throwing performance: A pilot study

Combining action observation (AO) and physical practice contributes to motor skill learning, and a number of studies pointed out the beneficial role of AO training in improving the motor performance and the athletes' movement kinematics. The aim of this study was to investigate if AO combined with immediate conventional training was able to improve motor performance and kinematic parameters of a complex motor skill such as the lineout throw, a gesture that represents a key aspect of rugby, that is unique to this sport. Twenty elite rugby players were divided into 2 groups. The AO group watched a 5-min video-clip of an expert model performing the lineout throw towards a target at 7 m distance and, immediately after the AO, this group executed the conventional training, consisting of 6 repetitions x 5 blocks of throws. The CONTROL group performed only the conventional lineout training. Intervention period lasted 4 weeks, 3 sessions/week. The AO group showed significant improvements in throwing accuracy (i.e. number of throws hitting the target), whilst no significant changes were observed in the CONTROL group. As concerns kinematic parameters, hooker's arm mean velocity significantly increased in both groups, but the increase was higher in AO group compared to CONTROL group. Ball velocity significantly increased only in the AO group, whereas ball angle release and ball spinning significantly decreased in both groups, with no differences between groups. Finally, no significant changes in knee and elbow angles were observed. Our results showed that the combination of AO and conventional training was more effective than a conventional training alone in improving the performance of elite rugby players, in executing a complex motor skill, such as the lineout. This combined training led to significant improvements in throwing accuracy and in hooker's and ball's kinematic parameters. Since AO can be easily implemented in combination with conventional training, the results of this study can encourage coaches in designing specific lineout training programs, which include AO cognitive training

Mechanical Spectroscopy and Structural Evolution of Thin CuMo Films

It is well known that in thin metallic films, the anelastic and the elastic properties show some characteristic features linked to the specific microstructure. The studied films Cu30Mo70, with a typical thickness of 200nm are deposited by Ion Beam Sputtering (IBS) on oxidised silicon (100) substrates. The measurements are performed on a vibrating reed device adapted for thin adherent films over a temperature range between 20°C and 450°C. This paper reports the combined results of internal friction, elastic modulus and internal stresses measured during thermal cycling. "Direct" observations of the microstructure are performed by X-Ray diffraction. We have correlated the modifications of the mechanical properties with the structural evolution of these metastable systems

NiTi and CuAlNi Martensite Studied by Isothermal Mechanical Spectroscopy

Intemal friction has been measured in isothermal conditions over a large frequency range (5x10-4 Hz-40 Hz) in NiTi (49.6 at.% Ni) and CuAlNi (12 wt.% Al, 3 wt.% Ni) alloys. A low frequency increase which depends on temperature has been found on NiTi sample in the martensitic phase. This damping effect has been ascribed to interface motions between martensite variants. As to confirm that the process is linked to the martensitic structure, CuAlNi al!oy was also studied. It has been observed that the low frequency damping behaviour of two samples looks totally different whether the sample has been slowly cooled from 1073 K or if it has been water quenched. Indeed, the low frequency increase is clearly evidenced in the first case contrarily to the water quenched sample where the effect is reduced and delayed as it appears only at much higher temperature. Several annealings have been performed on the quenched sample and the ageing effects have also been observed by modifications on the internal friction level. In addition, the structural evolution of this last sample has been observed by X-ray diffraction experiments

Thermal Cycling Effect on the Premartensitic and Martensitic Transition in a Ti Rich NiTi Alloy

The study was carried on a Ti-rich NiTi shape memory alloy. The electrical resistance and the elastic modulus were determined versus temperature. The aim of this work is to study the thermal cycling effect on the transformation features as the temperatures or the phase succession as well as the structural modifications. The major results of this work concern the R-phase occurrence and its evolution. We have shown that the premartensitic phase could exist in a narrow range of temperature on cooling and is revealed only after a few cycles. In fact, its presence and stability is directly linked to the diminishing of Ms. The main condition for the austenite to be transform in a rhombohedral structure is that Ms becomes low enough to be below Tr. Intempted cooling runs also show that contrarily to the austenite-martensite transition, the austenite-R-phase transition doesn't exhibit any hysteretic behaviour

High Temperature Internal Friction in Ni Ti Alloy

Former internal friction studies concerning NiTi alloys are currently limited to the temperature range 300 K-400 K relative to the martensitic transition. This paper describes results obtained by isothermal mechanical spectroscopy between 400 K and 1050 K with a sample in austenitic phase after different thermomechanical treatments : cold rolled, deformed by tension, submitted to successive transition cycles or annealed at high temperature. Two relaxation peaks superimposed to a low frequency (i.e. high temperature) background were found. For the first one (520 K at 1 Hz) both, the variation of the relaxation strength with the measurement temperatures and the relaxation parameters (Ea = 1.35 eV and τo = 2.5x10-14 s) correspond to a Zener relaxation. The high temperature peak (870 K at 1 Hz) was associated with a relaxation due to dislocation segment motion

First stage of the structural evolution of austenite in Cu-Al-Ni shape memory alloys

Two shape memory Cu-Al-Ni alloys, a polycrystal and a single crystal, exhibiting a martensitic transformation close to 130 °C (in the as-quenched state) have been studied. Specimens have been quenched after heat treatment at 850 °C. The structural evolutions of the high temperature phase (austenite) have been studied for thermal treatments performed below 200 °C. Investigations have been carried out using electrical resistivity measurements, TEM (Transmission Electron Microscopy) observations and X-ray diffraction analysis. The main structural modifications are observed in the polycrystalline alloy and concern first, the reordering process of the austenite structure (B2$\to$L21), and second, the precipitation of the (Cu9Al4) γ2 phase. In the single crystal alloy, the evolutions are very slight and localized on the structural defects. Particular attention is paid to the role of the quenched-in vacancy elimination on the observed mechanisms. In addition, the incidence of the structural evolution on the transformation temperatures is also discussed