Investigations on the Thermo-Mechanical Properties of CrN/CrCN Gradient Coatings Using a Thermo-Dilatometric Method

The paper describes issues related to the use of dilatometric methods for the study of thermo-mechanical properties of PVD gradient coatings. Tests were conducted on three types of CrCN / CrN coatings, which differed in the nature of the change of physico-chemical parameters in the gradient transition layer, deposited on a molybdenum substrate with the use of the cathodic arc evaporation method. The scope of the experimental studies included an analysis of the changes of the thermal “extortion” of the substrate – PVD coating system during annealing processes. In parallel, for comparison purposes, a mathematical description was proposed of gradient coatings containing the transition functions of material parameters. These functions describe the changes of such parameters as the Young's modulus, the Poisson's ratio, the thermal expansion coefficient, and the density as a function of spatial variables. Using the mathematical description proposed, numerical calculations of the state of thermal stress and strain for coatings are represented, respectively, by the transition function forms (a stepped, square, and square root) were carried via FEM. Based on the experimental and computational results obtained, the comparison between the elongation of the tested samples, and the state of thermal stress and strain in the substrate-gradient coating systems analysed were all specified.

Design and Test for a High-Temperature Molten Salt Pump

A high-temperature molten salt pump, described as mechanical, free-surface, centrifugal, vertical-shaft, sump type, working at 500°C [932°F] to 600°C [1112°F], has been developed for the Thorium-Based Molten Salt Reactor (TMSR). Flow passage components of the pump are made of Hastelloy C-276 to ensure sufficient strength and corrosion resistance at high temperature. Also, a heat shield plug with air-cooled channels was designed to separate the drive motor, seal elements, and bearings from intense radioactivity and to keep the temperature of the flange seal below 150°C [302°F] and the temperature of the bearing below 80°C [176°F]. A dry gas seal was used so that there is zero leakage. Furthermore, some analysis of hydraulics characteristics, temperature field, thermal stress, and strain was performed to research the pump’s performance, and then the temperature field and the hydraulics were measured to validate the analysis results. The results show that the hydraulics, thermal stress, and strain meet the design value very well. The pump has been successfully operated on a LiF-NaF-KF test loop for over 250 hr. at temperatures of 500°C [932°F] to 600°C [1112°F], speeds of 1050 to 1450rpm, and flows of 15 m3/h [66 gpm] to 25 m3/h [110 gpm]. Paper published with permission.

Steady thermal stress and strain rates in a rotating circular cylinder under steady state temperature

Thermal stress and strain rates in a thick walled rotating cylinder under steady state temperature has been derived by using Seth?s transition theory. For elastic-plastic stage, it is seen that with the increase of temperature, the cylinder having smaller radii ratios requires lesser angular velocity to become fully plastic as compared to cylinder having higher radii ratios The circumferential stress becomes larger and larger with the increase in temperature. With increase in thickness ratio stresses must be decrease. For the creep stage, it is seen that circumferential stresses for incompressible materials maximum at the internal surface as compared to compressible material, which increase with the increase in temperature and measure n.

Study on Alleviating Thermal Stress of Piston Head

In order to alleviate thermal stress of piston head, the causes of thermal stress are studied. The original piston is modified from the perspective of easing strain concentration. The thermal stress and strain fields of the original and modified pistons are analyzed with FEM. Comparison of the analysis results shows that analyzing strain concentration is an efficient way to find out the fundamental causes of high thermal stress of piston head. Thus viable approaches are proposed to solve the problem.