Formation and Dissolution of γ’ Precipitates in IN792 Superalloy at Elevated Temperatures
Precipitation of γ’ phase in nickel-base superalloy IN792-5A was studied using in-situ Small Angle Neutron Scattering (SANS). It was found that additional precipitates are formed after reheating above 600 °C when the material is previously fast cooled (100 K/min) from 900 °C. The size distribution and volume fraction of the additional γ’ precipitates as well as of the already present medium-size precipitates in dependence on temperature were evaluated. The small precipitates can influence mechanical properties of the alloy, which exhibits an anomaly in the temperature dependence of the yield stress. Volume fraction of all precipitate populations above 900 °C was estimated as well.
A modelling approach to yield strength optimisation in a nickel-base superalloy
Abstract A computational methodology combining models of precipitation and dispersion strengthening with grain growth and grain boundary hardening has been produced to provide a predictive capability of the microstructure and yield strength of nickel-base superalloys subjected to arbitrary thermal cycles. This methodology has been applied to optimise the post-forging heat treatment of the advanced polycrystalline nickel-base superalloy, RR1000, to provide an improved proof stress. The temperature dependent antiphase boundary energies required were obtained using thermodynamic data and temperature dependent lattice parameters obtained via in situ synchrotron X-ray diffraction. Optimal yield strength properties between 600 and 700 °C were predicted with precipitates in the range of 34–57 nm. The precipitation modelling software, PrecipiCalc was used to optimise the solution and ageing heat treatments to maximise the volume fraction of intragranular γ ′ precipitates within the target precipitate size range, whilst maintaining a critical minimum volume fraction of primary γ ′ to give a grain size of 7 μm. The optimal yield strength of the material was predicted following a heat treatment consisting of 4 h at 1105 °C; cooling to ambient at 40 °C s−1, and ageing for 16 h at 798 °C. Tensile testing at 650 °C of samples subjected to this heat treatment showed a 125 MPa increase in yield strength over RR1000 in the conventional microstructural condition. However, this was accompanied by a significant loss of ductility.
Application of 2μm Tm Laser on Biomedicine
Continuous wave Thulium laser emits at wavelength of 2.0 mm, which is well suited for tissue ablationand thermally stimulating cutaneous nerves due to its high absorption by water. 2 mm laser can be transmitted suffi-ciently by common quartz fibers and it is safe for eyes. A brief introduction of principle of 2 mm CW Tm Laser is giv-en, analyzing the photothermal modeling of thulium laser-tissue interaction, comparing 2 mm CW Tm Laser with tradi-tional laser.