Papers by Keyword: Thermal Shock

Abstract: Ti alloys are applied extensively in several fields, particularly in the aerospace, chemical, dental and medical industries, due to their outstanding properties. Microstructure changes in commercial-purity titanium (CP-Ti) during open flame thermal shock and X-ray analysis were investigated. Water quenching of compact Cp-Ti has yielded martensitic-type laths and fishbone-type twinned microstructures. The microstructure of cast samples displays a martensitic structure and heat-treated samples shows a microstructure composed of α/α^‘phase. Several types of phases and crystallographic lattice were detected using XRD. Samples investigated were supposed to a heating over than 1500°C and cooled in two ways: by air and by water. SEM images are taken in comparison for studying the morphology and microstructure of alloys.

Abstract: NiCr/ZrO₂ gradated coatings were obtained on C45 carbon steel by high velocity arc spraying and micro-plasma spraying to improve the mechanical and thermal behaviors of the carbon steel. Scanning electronic microscope (SEM) and X-ray diffraction (XRD) were employed to characterize the microstructure of the prepared composite coatings. Mechanical properties including hardness and bonding strength were also evaluated by microhardness tester and electron tensile tester. The thermal shock behaviors were investigated by quenching the coating samples in cold water from 900 °C and 1100 °C, respectively. The oxidation of NiCr/ZrO₂ gradated coating and C45 carbon steel substrate were carried out for up to 108 hours in air atmosphere at 1100°C. The oxidation behaviors were investigated after detailed examinations by thermal gravimetric analysis. Experimental results indicate that NiCr/ZrO₂ gradated coating exhibit a much higher hardness and high temperature oxidation behavior than the substrate. The bonding strength and thermal shock behavior of NiCr/ZrO₂ are superior to pure ZrO₂ coating, which could be mainly attributed to the NiCr intermediate graded layer due to the microstructure improvement and relaxation of residual stress concentration.

Abstract: Mullite material is a material commonly used in honeycomb regenerator, because in the process of using material under big temperature difference effect, so have a great demand for its thermal shock resistance. The used mullite ceramics were made by the direct solid phase sintering method, and the modulus of elasticity of the mullite ceramics measured by ultrasonic pulse-echo method in a thermal shock and thermal fatigue experiment, respectively. In the air-cooling condition, the study found the mullite ceramic without thermal shock that the longitudinal wave velocity and shear wave velocity respectively 3970(m/s) and 2492(m/s). After 45 times thermal shock of temperature difference of 800°C, longitudinal wave velocity and shear wave velocity decreased to 3910(m/s) and 2457(m/s), and the value of the modulus of elasticity changed 1020MPa. By observing the change of the elastic modulus value rule, can know the elastic deformation of thermal shock on the material performance of thermal shock damage. Moreover, the results can provide the data basis for the calculation of the residual strength and the numerical simulation of thermal stress.

Abstract: For study the damage characteristic of the mullite heat storage ceramic under thermal shock condition, mechanical properties of mullite have been investigated. Under the different cooling mediums (room temperature water, boiling water, air), single and five cycles thermal shock conditions, The article studied the variation of flexural strength and fracture toughness along with temperature. The result show that with the increase of heat transfer coefficient of cooling medium, the bending strength of ceramic decreased. In the 600°C,the ceramic have a maximum bending strength and a minimum fracture toughness. The fracture toughness of precrack specimen is lower than that of non-precrack specimen on the whole. Both Precrack ceramic and non-precrack ceramic have a maximum fracture toughness at 400°C. The study of this paper provides a theoretical basis for the better predicting fracture damage and service life of heat storage ceramic.

Abstract: Cordierite ceramics are known for their low CTE and high compressive strength values which affords them place in fields where demanding thermal and mechanical properties are required. Development of such ceramics is greatly dependent on materials used. If raw materials are used formation of additional phases and pore/glass formation is expected. The purpose of this research is to examine the process of cordierite development from mixed compositions formed from precursors of the natural raw materials as illite clay, dolomite and quartz sand and synthetic additives – MgO, γ-Al₂O₃ and their influence on thermal and mechanical properties. It is verified that the addition of 10 wt.% of illite clay and about 20-21 wt.% dolomite in staring compositions at the sintering temperature of 1200 °C results in the development of dense ceramic material with perfect-shaped crystalline cordierite phase and secondary anorthite phase. Sintered cordierite ceramics have been tested, among other properties, for their compressive strength, coefficient of thermal expansion and modulus of elasticity after 20 cycles of thermal shock treatment.

Abstract: The paper is a practical study, in which the authors have proposed to improve the reliability in operation of hot work tool steels, used for the manufacturing of seamless steel tubes.There were developed samples of hot work tool steel with different chemical compositions by micro-alloying with Mo. The samples were studied in order to investigate their structure and the relations between the microstructure and in-situ behavior.

Abstract: Failure of steam-side oxide scales in high temperature components of boilers such as superheater and reheater tubes has significant effect on the safety of thermal power plants. Finite element analysis is carried out to investigate the failure issues of steam-side oxide scales in boiler tubes during thermal shock processes. The effects of different steam temperature variation durations on oxide scale failure issues have been analyzed. According to the results, appropriately lengthening variation duration can contribute to relieving oxide scale failure issues, and are subsequently proposed.

Abstract: (TiAlZrNb)N hard reactive films are prepared by multi-arc ion plating technology using the combination of Ti-18Al-11Zr (at%) and Ti-25Nb (at%) alloy targets. The high speed steel (HSS) is adopted as substrate. The surface and cross-fracture morphology, the surface compositions and the phase structures of the as-deposited (TiAlZrNb)N films are observed and measured by scan electronic microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The mechanical properties including micro-hardness, adhesion between film and substrate, friction and wear resistance and thermal shock resistance of the as-deposited (TiAlZrNb)N films are systemically investigated. The effects of deposition bias voltage and the addition of Nb element on the as-deposited (TiAlZrNb)N films are discussed. It is revealed that the comprehensive performances including micro-hardness, adhesion and friction resistance can be achieved by the (TiAlZrNb)N hard reactive film with deposition bias voltage of 150V.

Abstract: Die casting is a cost-efficient method of forming geometrically complex near net-shaped products with close tolerances and excellent surface finishes.Due to the thermal shock characteristics, a number of test methods have been proposed to understand thermal fatigue behaviours of the die material as real die casting dies experience.This study reveals the differences of these methods by numerical modelling the thermal behaviour of the test specimen. Simplified die casting process is firstlyproposed to facilitate numerical computation. Test specimens are then optimized to be more representative of a real die. From the comparison results, we can conclude that least divergence can be obtained between immersion tests and induction heating based tests while furnace heating based tests would result in low thermal shock effects on the test sample.

Abstract: (TiAlNb)N hard reactive films are prepared by multi-arc ion plating technology using the combination of Ti-50Al (at%) and Ti-25Nb (at%) alloy targets. The high speed steel (HSS) is adopted as substrate. The surface and cross-fracture morphology, the surface compositions and the phase structures of the as-deposited (TiAlNb)N films are observed and measured by scan electronic microscope (SEM) and X-ray diffraction (XRD). The mechanical properties including the micro-hardness, the adhesion between film and substrate, the thermal shock resistance of the as-deposited (TiAlNb)N films are systemically investigated. The effects of deposition bias voltage and the addition of Nb element on the as-deposited (TiAlNb)N films are discussed. The optimally comprehensive performances, especially hardness and thermal shock resistance, exhibited by (TiAlNb)N films with bias voltage of 100V.