Cyclic overaging heat treatment for ductility and weldability improvement of nickel based superalloys

Abstract

A new cyclic overaging heat treatment for ductility and weldability improvement of advanced nickel based superalloys has been investigated. The heat treatment consists of intermittent heating cycles during the cooling stage to check the nucleation of fine γ' in the material during the overaging. Using Rene 80 alloy as a model material, the effects of intermittent heating rate and duration were studied and optimised. Quantitative metallography was carried out to compare the microstructures produced by the proposed heat treatment with those produced by other conventional pre-weld heat treatments. Tensile tests and welding tests both showed that the proposed cyclic over-aging heat treatment is effective in improving the tensile ductility and weldability of Rene 80 alloy.     

Review of rejuvenation process for nickel base superalloys

Abstract

Combustion turbine components exposed to elevated temperatures and high stresses are subject to periodic replacement as a result of mechanical property degeneration to levels below that required for continued safe operation. In view of the very significant cost associated with replacement components there has been much interest in the rejuvenation of parts. This report reviews published literature on the rejuvenation of nickel base superalloys. The restoration of microstructure and properties to levels equivalent to the original material have been achieved with the use of reheat treatment alone or recovery cycles incorporating both hot isostatic pressing and reheat treatment. The majority of the literature considers the restoration of creep properties, although some success in the rejuvenation of fatigue properties has also been reported.     

A heat exchanger model for air-to-refrigerant fin-and-tube heat exchanger with arbitrary fin sheet

A new model for simulating air-to-refrigerant fin-and-tube heat exchangers, with arbitrary fin sheet which encompasses variable tube diameters, variable tube locations, variable tube pitches, internal as well as external jagged edges, variable number of tubes per bank and variable location of fin cuts, is introduced. This model is based on a segment-by-segment approach and is developed to be a general purpose and flexible simulation tool. To account for fin conduction and air propagation through the heat exchanger, it is spatially modeled on a Cartesian grid. A new methodology for air side propagation, required for arbitrary fin sheets, is introduced. The model prediction is validated against experimental data for a condenser using R410A as the working fluid. The predicted results agree within ±5% of overall heat load, and ±25% for total refrigerant pressure drop.     

MoSi2及MoSi2基材料的强韧化

MoSi2以其较高的熔点、适中的密度和优异的高温抗氧化性能而成为近年来倍受关注的金属间化合物,但其室温脆性和低的高温强度是限制其应用的主要原因. 从合金化和复合化等方面对MoSi2及MoSi2基高温结构材料的强韧化作了概述.     

V形布置换热器性能优化

采用数值模拟方法,对某风冷模块式冷水机组的V形布置换热器气流组织和传热性能进行研究和分析。研究表明,V形布置换热器间夹角的适当增加,可改善气流在换热器表面分布的均匀性,提高换热器换热性能,进而有助于制冷系统性能的提升。     

Selecting elastomers for plate heat exchanger gaskets

Plate heat exchangers have recently become more versatile, due in part to the availability of suitable elastomers for gaskets.     

Application of high temperature DSC technique to nickel based superalloys

Heat capacity is a critical input parameter in mathematical models of solidification and casting. It appears in its own right, and is required for the extraction of thermal conductivity from thermal diffusivity data. It also provides a measure of the latent heat associated with changes of phase, and the precipitation or dissolution of precipitates. Calorimetry is a well-established technique and is used to solve a wide range of materials problems such as studying precipitation or phase changes in alloy systems, and the kinetics of these phase transformations. The quality and range of data that can be obtained will be demonstrated by applying it to nickel base superalloys.This paper discusses important aspects of the measurement including control of the atmosphere, suitable reference materials for temperature and enthalpy calibration, size of the sample and the rate of heating and cooling. The optimised DSC technique was used to investigate the properties of two nickel based superalloys (CMSX4 and IN738LC), comparing the results with previous values and determining sources of error in the method.     

Hot forging behavior of nickel based superalloys under elevated temperatures

Thermomechanical behaviors of superalloys at high temperatures and constant strain rates related dynamic microstructural changes are studied in this article by means of the commentaries of thermomechanic graphs and microdublex changes. Thermomechanic and microdynamic deformation characteristics based on test data are presented by a methodology for superalloys which are consolidated by hot isostatic pressure (HIP) operation. It is assumed that true stress which is caused deformation, changes depending on thermomechanical behaviors such as; strain, strain rate, absolute temperature, activation energy, diffusion mechanism, grain size, microdynamic behaviors and structural parameters of the material. In this study, a detailed investigation of thermomechanical and microdynamical behaviors of powder metallurgy (PM) Rene 95 is carried on by the attribution of experimental data.     

Precipitation hardening in nickel based superalloys: effect of alloying

Abstract

The growth kinetics of γ′ precipitates in Ni based wrought superalloys was investigated, using a computer aided X-ray analysis method. It was found that the growth process obeys the Lifshitz–Slyozov–Wagner law. Regression formulae describing the liquidus, solidus, and γ′ solvus temperatures as functions of the overall composition were established. The heat treatment window as a function of composition and its effect on homogenisation and retained hardness were determined. The high retained hardness of homogenised Al + Ti rich alloys hinders their commercial use as Ni base wrought superalloys.

MST/3206     

空调排风能量回收用热管换热器的优化设计

对用于回收空调排风热（冷）量的热管换热器的整体优化设计进行研究,提出对其整体优化的设计方法,建立寿命期总经济效益最大为目标的目标函数,并利用标准气象年数据,研究不同温度下的热管换热器的最优结构,通过经济性分析,得出整个供暖（冷）季的最优结构和最佳经济性能的热管换热器.     

Optimisation of a salt deposition technique for the corrosion-fatigue testing of nickel based superalloys

This paper summarises the work undertaken to develop a salt deposition technique that can be utilised for hot corrosion and high temperature corrosion-fatigue testing of high performance alloys for gas turbine application. The optimisation process has yielded a new method of application of a sodium sulphate based solution to various test piece geometries. The technique employs the use of a micro-pipette to deposit a pre-calculated solution, consisting of methanol, water, Na₂SO₄–NaCl onto preheated specimens, in preparation for corrosion testing. This optimised salting technique has reduced the variability in the salting of test specimens, when compared with existing salt spray methods and has therefore enabled test repeatability along with an associated significant reduction in scatter within high temperature corrosion-fatigue results.     

Process optimisation of selective laser melting using energy density model for nickel based superalloys

The main challenge associated with the application of selective laser melting (SLM) to Ni based superalloys is the performance of process optimisation to maximise the mechanical properties. The energy density parameter has typically been used as a semiquantitative approach to identify the energy threshold beyond which the material achieves virtually full consolidation. Nonetheless, some Ni superalloys are susceptible to crack formation during SLM, which cannot be avoided via process optimisation. In the present report, a comparative study is presented showing the utility of the energy density parameter in process optimisation for γ′ and γ′/γ″ strengthened Ni based superalloys. For both classes, it was found that the build density increases [i.e. void area (%) decreases] with the increase in the energy density. Nonetheless, no direct correlation can be found between the energy density parameter and the cracking density.     

板翅式换热器的传热计算

介绍了板翅式换热器的结构形式,通过传热方程式推导出了翅片效率、表面效率以及流动阻力的计算公式,为板翅式换热器的计算提供依据。     

管壳式换热器的经济学优化设计

本文对管壳式换热器的火用经济特性进行了分析与计算，对以单位收益火用成本最低为目标的换热器优化设计，给出了适于工程设计的计算方法。     

微通道换热器研究进展

从微通道换热器的发展历史出发,介绍其制造方式、结构和材料,重点介绍对微通道换热器发展和降低成本有重要影响的全铝微通道管材成形加工技术。对微通道传热的特征进行述评,从微电子微机械高效传热、CO2制冷减少温室气体排放和提高家用空调能效比几个方面展现微通道换热器的应用前景。     

家用热泵空调器室外机换热器的流路优化

针对家用热泵空调器用的9.52 mm和7 mm双排室外换热器,在额定制冷制热工况下,利用仿真分析的方法研究流路数对换热器性能的影响,对9.52 mm换热器的流路的进一步优化,得到制冷制热综合性能更优的流路布置方式,并在整机上进行试验验证。结果表明,制冷剂侧压降对冷凝器和蒸发器的换热都有较大影响,特别是对较小管径的换热器;由于蒸发器中制冷剂侧压降较大,热泵空调器室外机用的换热器作冷凝器时对应的最佳流路数少于作蒸发器时的;适当增加过冷管数会进一步提高热泵空调器室外机换热器的综合换热能力;试验结果与仿真结果趋势大致相同。     

Experimental investigation on performance of desiccant coated heat exchanger and sensible heat exchanger operating in series

As a novel solid desiccant component, solid desiccant coated heat exchanger (DCHE) is proposed by coating solid desiccant material to conventional sensible heat exchanger (SHE) surface. The idea of adopting a DCHE and an SHE operating in series is proposed and an experimental setup was built up to investigate its performance. Results show that with the use of an auxiliary SHE, the temperature variable rate increases, while about 4 °C lower outlet temperature can be obtained, the corresponding cooling power and COP increase by about 75% and 13% respectively. Besides, lower cooling water temperature is recommended to obtain enhanced system performance; system performance increases with increasing inlet air temperature and relative humidity ratio, the recommended air velocity is different with respect to different aims.     

Efficiency of an air heat exchanger

Experimental and calculated dependences of the coefficient of thermal efficiency of a heat exchanger are presented for various effective diameters of the internal channels. It is shown that a region of a local maximum of the coefficient of thermal efficiency exists in the regime of a turbulent flow of the coolant. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 1, pp. 97–102, January–February, 1998.