铝基体化学镀镍对热障涂层抗热震性影响研究

研究了铝基体化学镀镍对热障涂层抗热震性能影响，结果表明，结构相同的热障涂层，基体经化学镀镍后涂层抗热震性由原来的35次剥落失效增长到200次无明显变化，这主要是因为化学镀镍层有效减缓了热障涂层和铝基体界面位置的热应力，并大幅度提高了基体的抗氧化能力，同时热震过程中镀镍层两侧界面位置的元素扩散提高了界面结合力，涂层抗热震性提高。     

A review of the high temperature oxidation of iron- manganese- aluminium alloys

Research on the oxidation behaviour of alloys from the Fe-Mn-Al system has been devoted primarily to the austenitic alloys with particular attention being paid to their mechanical properties. Information regarding their oxidation behaviour and scale morpology is sparse. There is very little on the behaviour of the ferritic alloys and these show great promise as heat resisting alloys, particularly with small additions of chromium. The oxidation behaviour of iron, manganese and binary iron-manganese alloys is reviewed in this paper, to clarify the behaviour of the more complex ternary alloys.     

Modifying the properties of the Inconel 625 nickel alloy by glow discharge assisted nitriding

The nickel alloys of the Inconel type (containing above 15wt% of chromium), used in many industrial applications including the manufacture of aircraft, chemistry, power generation, and material processing, have advantageous mechanical properties, high plasticity and good corrosion resistance, but their frictional wear resistance is poor. This drawback can be obviated by subjecting the alloys to various surface treatments.The paper describes the structure and properties of nitrided layers produced on the Inconel 625 nickel alloy (20wt%Cr, 10wt%Mo, 5wt%Fe, 1wt%Co, balance-Ni). It has been found that the diffusion-type chromium nitride layer produced on the alloy surface improves the hardness, frictional wear resistance, fatigue strength and corrosion resistance of the alloy. It was demonstrated that the nitriding process can be successfully used for prolonging the service life of the fiberizing disc intended for the fabrication of what is known as glass wool.     

Experimental and numerical investigation of thermal loads in Inocnel 718 machining

Inducing high thermal loads in machining of difficult-to-cut materials changes the mechanical properties of a machined surface/subsurface. In particular, a thermally affected layer leads to tensile residual stresses and microstructure changes. Nickel-based alloys are hard materials and frequently used in different industries. Since the generation of thermal loads in machining Inconel 718 is evident, in this paper an experimental and numerical investigation were performed to evaluate thermal loads and the depth of the affected layer in the machining of Inconel 718 superalloy. First, the effect of cutting parameters was studied on the average machined surface temperature by experimental tests. Then, the results of experiments were used to validate a 3D numerical model. Using the calibration strategy, the heat transfer coefficient at the chip–tool interface was found to be dependent on the cutting conditions. Next, the effect of the initial workpiece hardness and tool geometry, including tool nose radius and edge radius, was evaluated on thermal loads and the depth of the recrystallized layer. The critical strain criterion was used to estimate the depth of the recrystallized layer and then, the numerical results were compared with experimentally measured depth of the affected layer at different machining parameters.     

Analysis of first mode metal transfer in A413 cast aluminum alloy during friction stir processing

Friction stir processing (FSP) is a recent processing technique where a non consumable rotating cylindrical tool is used to generate frictional heat and local plastic deformation at selected processing locations. In cast alloys, FSP eliminates casting defects and refines micro structures, and leads to improvement in their mechanical properties. The metal flow phenomenon in friction stir processing (FSP) comprises two modes of metal transfer. The first mode of metal transfer takes place layer by layer and is caused by the shearing action of the tool shoulder, while the second mode is caused by the extrusion of the plasticized metal around the pin. The aim of the present study is to quantitatively determine the amount of metal transferred by the first mode during friction stir processing of cast aluminum A413 alloys and its influence on the tensile properties. The experimental results show that the mechanical properties can be enhanced through FSP and the enhanced properties have good correlation with the first mode of metal transfer.     

铸造铝硅系合金的时效研究与应用进展

围绕铸造铝硅系合金,基于国内外文献调研,综述了当前国内外的时效研究与应用进展.通过调整合金成分、改善热处理工艺等方式可以调控铸造铝硅系合金中析出相的形貌与分布,从而改善合金的性能以满足工业应用的需求.在现有的时效处理工艺中,主要分为单级时效、双级时效以及回归再时效.在此基础上着重分析了不同时效工艺下铸造铝硅合金的组织及...     

Er对ZrCuNiAl非晶合金结构、力学性能、热稳定性及非晶形成能力的影响

以(Zr_0.6336Cu_0.1452Ni_0.1012Al_0.12)_100-xEr_x(x=0,0.5,1,1.5,2,2.5,3,原子分数,下同)系块体非晶合金为研究对象,通过改变微量元素Er的含量来研究Er对非晶合金的结构、力学性能、热稳定性及非晶形成能力的影响。结果表明:添加Er元素所制备出的试样都是完全非晶结构的合金。随着Er含量的增加,各试样的弹性模量呈现出先增大后减小,压缩塑性应变呈台阶式上升,x=0,x=0.5,x=1试样的塑性应变在4%的范围内波动;x=1.5,x=2,x=2.5试样的塑性应变在11%的范围内波动;x=3试样的塑性应变最高,其值为23.19%,弹性模量为37.76GPa,屈服强度为1604MPa,抗压强度为2068MPa,断裂强度为2060MPa;随着Er含量的增加,锆基非晶合金的热稳定性和非晶形成能力均先减小后增大。     

Gefüge und magnetische Eigenschaften von Chromgusseisen für Mahlkugeln

Microstructure and magnetic properties of white cast irons for grinding balls Many types of cast ferrous alloys are used for applications in the grinding, crushing, mineral‐handling and earthmoving industries. The finish grinding process for cement materials uses ball mills with differently sized grinding balls. This work deals with grinding balls of high chromium white cast irons with various chemical composition. Using certains thermal treatments, the influence of parameters of microstructure on abrasive and impact wear resistance has been studied. A special test system has been adapted for the assessment of the impact properties of these alloys. Examination of the carbides were performed using a transmission electron microscope. Additional microstructural examinations were made using the Scanning electron microscope. For a nondestructive inspection of the grinding balls, the possibilities of using the magnetic characteristics for determining the structural state and mechanical properties of white cast irons are analyzed. The results showed that the hardness and the dynamic fracture toughness are important for the combined impact‐abrasion resistance. It has been established that the microstructure has a decisive influence on the magnetical properties of white cast irons.     

An investigation into the tribological performance of Physical Vapour Deposition (PVD) coatings on high thermal conductivity Cu-alloy substrates and the effect of an intermediate electroless Ni-P layer prior to PVD treatment

The use of high thermal conductivity copper alloys in plastic injection moulds provides the benefit of rapid moulding cycles through effective heat transfer. However, copper alloys are relatively soft and wear rapidly so manufacturers are now developing copper alloys with increased hardness and wear resistance. Their wear resistance can be further improved by the deposition of hard coatings such as electroplated chromium, electroless nickel and Physical Vapour Deposition (PVD) coatings. In this paper, the tribological performance of three proprietary high-strength Cu alloys (Ampcoloy® 940, Ampcoloy® 944 and Ampcoloy® 83) coated with PVD CrN and CrAlN coatings has been evaluated. A medium phosphorous content electroless Ni-P (ENi-P) plated layer was also deposited as a pre-treatment to PVD CrN and CrAlN coatings to increase the load support. The effect of this intermediate ENi-P layer was also evaluated. Surface roughness and instrumented hardness measurements were used to characterise all coated systems in both plated (i.e. with the intermediate ENi-P coating) and standard (i.e. unplated) conditions. Scratch tests were also performed to evaluate the effect of the ENi-P on PVD coating adhesion to Cu alloy substrates. The tribological behaviour of PVD-coated Cu alloy systems was evaluated by pin-on-disc wear tests and ball-on-plate impact tests. Results demonstrate that the ENi-P layer improves the load support for PVD coatings on Cu alloys, thereby improving their tribological performance. However, for PVD-coated Cu alloys in the standard condition, the Cu alloy substrate type plays an important role in the tribological performance of PVD coatings. For instance, PVD CrN coatings were more suited to a certain Cu alloy type whilst CrAlN to the other two types.     

Microscopic analysis of Fe–Cr alloy produced by single roll strip casting

Abstract

In the present investigation, the microstructures and mechanical properties of Fe–Cr alloy prepared by single roll strip casting were studied. Optical microstructure showed subgrain boundaries inside large grains. Cracks were observed along the grain boundary. Scanning electron microscopy, X-ray diffraction study confirms the formation of chromium carbide at the grain boundary in the case of as cast alloy. Electron backscatter diffraction showed preferred orientation of grains in the as cast alloy. Carbides and undesired phases were not observed in heat treated alloy. Pores present in as cast samples expand after heat treatment process. Mechanical properties, like tensile strength, yield strength, elongation and hardness, of Fe–Cr single roll strip casting alloys were improved after heat treatment.     

High temperature carbon corrosion in solid oxide fuel cells

Abstract

Operating conditions in a current design for a planar geometry oxide fuel cell plant are briefly reviewed and the danger of encountering “metal dusting” conditions identified. Laboratory tests were designed to produce accelerated metal dusting by exposing heat resisting alloys to a CO–26 H₂–6 H₂O (vol. pct) gas mixture at 680°C under thermal cycling conditions. The hot gas composition corresponded to a_c = 2.9 and an oxygen potential high enough to oxidise chromium and aluminium, but not iron or nickel. The alloys tested included ferritic and austenitic chromia formers and two ferritic alumina formers, all with electropolished surfaces. Thermal cycling of the chromia formers led to oxide scale damage followed by internal carburisation, metal dusting and coking. This failure occurred very rapidly on most austenitic materials (Alloy 800, Inconel 601, 690, 693, Alloy 602CA), but did not commence until after approximately 50 one-hour cycles for the ferritic steel Fe–27Cr–0.001Y (wt %). The alloy with the best performance was Inconel 625, which was still protected by its Cr₂O₃ scale after 500 cycles. The alumina forming alloys showed superior performance, with no damage apparent after 1200 cycles. Additional tests using ground metal surfaces showed that they were more resistant to dusting in the case of chromia formers, but more susceptible in the case of alumina formers, metal dusting.     

Effect of top and bottom filling on reliability of investment castings in Al,Fe, and Ni based alloys

Abstract

The effect of bottom and top filling running systems on the properties of four investment cast alloys susceptible to contamination by oxide films during filling was studied. The alloys were air cast 2L99 Al–Si–Mg alloy and 254-SMO super duplex stainless steel and vacuum cast IN939 and IN738LC nickel based superalloys. The Weibull moduli for the tensile strength of investment cast bars produced using top and bottom filling were compared as indicators of casting reliability and of oxide damage produced by the running systems. A Weibull modulus of 18 was obtained for top filled 2L99 castings; this was increased to 34 when a correctly designed bottom filling system with a filter was used, thus reflecting the decreased scatter in properties. However, a similar effect was not found for the stainless steel. The use of improved running system designs led to minor increases in the Weibull modulus of the IN738LC and IN939 Ni alloys.     

Improvement of mechanical properties of chromium–nickel sintered compacts by multiple rolling

The present paper provides details on the thermomechanical treatment of chromium–nickel alloys with high content of chromium, which leads to considerable improvement of their mechanical properties. The investigated alloys were prepared from Cr–Ni powder mixtures containing 50% and 80% of chromium in mass. They were formed by a particular sequence of cold and hot isostatic pressing. The as-sintered compacts were essentially brittle at room temperature, while they have exhibited considerable ductility after the special thermomechanical treatments. The treatment consisted of a sequence of repeated rolling and annealing operations, which is relatively simple and applicable in the industrial production. It is found that the treatments led to a more homogeneous, better alloyed structure and enhanced interdiffusion of the component metals.     

Thermo-mechanical fatigue resistance characterization and materials ranking from heat-flux-controlled tests. Application to cast-irons for automotive exhaust part

In a context where the mass, the cost and the mechanical strength of materials must be jointly optimized, it is necessary to have experimental data quickly available and sufficiently robust to make efficient conception choices. For thermomechanical fatigue, standard tests usually allow comparing material for the same temperature and strain ranges although differences in thermal properties such as conductivity or thermal expansion could make significant deviations when the same thermal flux is applied particularly for structure with forced heat flux operating regimes. A new protocol is then proposed in order to compare the specific resistances of metallic materials against thermomechanical fatigue. It can easily rank materials according to their lifetime under thermomechanical loadings where strain range and temperature amplitude are determined by the heat flux applied on an industrial part. The method is based on a complete numerical analysis to determine experimental loading conditions as a temporal evolution of temperature and mechanical strain representative of thermomechanical loading observed in TMF critical areas for the part. TMF tests on hollow specimens are carried out to rank the materials: temperature and strain amplitude are different for each alloys whereas heat flux is identical. A materials ranking list based on TMF resistance is then determined according to their lifetimes under “heat-flux-controlled” tests. The method is tested for exhaust parts and demonstrates the superiority of some cast irons over others, whereas the intrinsic isotherm mechanical properties suggested an alternative classification. The obtained ranking is confirmed by experimental tests on industrial structures.     

Modifizierte Nickelbasisstandardlote für korrosiv belastete Bauteile

Modified nickel based standard brazing filler metals for units under corrosive loads Nickel‐based alloys are presently used as brazing filler metals for components which undergo mechanical stress in corrosive conditions, f. e. heat exchangers. When soldering chrome containing steel parts with nickel based brazing filler metals additionally containing boron and silicon a reaction of chrome and boron can occur. This evolution of chromium borides, depositing on grain boundaries, causes a lack of chrome in the steel part. A drop of the chrome content in the parts below 13 % leads to a loss of corrosion resistance. It is possible to change the microstructure of brazing joints by modification with chromium and molybdenum. Continuous brittle phases could be successfully avoided with this modification. Furthermore it could be shown that the choice of additives, the heating respectively cooling rate and the brazing temperature have important influence on the microstructure evolution and therefore on the mechanical and corrosive properties of joints.     

High-temperature oxidation behaviour of base metal elements in nickel-base alloys

Oxidation of non-precious metals nickel, chromium and copper, nickel-base alloys in an air atmosphere was studied under differential thermal analysis. The results suggest that adding chromium and copper to high-purity nickel metal reduces the amount of oxidation and gives a slower oxidation than in untreated high-purity metals. It is then shown that the activation energy for oxidation in nickel-base alloys is almost the same as that in high-purity nickel metal when alloying elements are added to nickel.     

耐热球墨可锻铸铁

耐热球墨可锻铸铁是一种新型的耐热铸铁，具体工艺是在中硅耐热球铁铁水中加入适量合金元素及变质剂，使之在铸态下得到白口组织，再经过石墨化退火而得到球团状石墨。该铸铁胶中硅耐热球铁有更为良好的常温力学性能及高温抗氧化性。尤其重要是的，因其凝固与结晶方式发生了质的改变，铸铁的缩松倾向得以明显改善。     

Spray‐Deposited Al‐Si (Osprey CE) Alloys and their Properties

Osprey Metals Ltd. has developed a new family of lightweight, low expansion aluminium‐silicon alloys to suit electronic applications, containing between 30 and 70 wt.% aluminium. They are produced using the Osprey spray deposition process, which achieves homogeneous and isotropic properties. Their advantageous physical characteristics, combining low thermal expansion, high thermal conductivity and low density are particularly suited for packaging electronic circuitry. These CE (controlled expansion) alloys are easy to machine to tight tolerances using standard machine tools and they can be electroplated with gold, silver or nickel finishes without difficulty. This paper focuses on the measurement of mechanical (flexural strength) and thermo‐mechanical properties (CTE, thermal diffusivity and specific heat) of these alloys, carried out in collaboration with AMTT. The property measurements were consistent with those measured previously elsewhere, apart from the CTE values, which deviated significantly and were at variance with values predicted from a rule of mixtures. This discrepancy was resolved in a short follow‐up series of measurements carried out under conditions corresponding more closely to temperature equilibrium.     

具有分层损伤复合材料加筋与无加筋层合板热-机械力屈曲性态

基于复合材料一维剪切理论——Mindlin 理论, 给出了材料性质与温度有关的含分层损伤复合材料加筋和无加筋层合板的线性和非线性热-机械力耦合情况下的屈曲问题有限元分析方法, 并研究了含分层损伤的加筋和无加筋层合板的两种不同类型的热- 机械力屈曲问题。通过典型算例分析, 讨论了热-机械力耦合效应和分层大小对含分层损伤结构的屈曲性态的影响关系。     

A hybrid arc spray forming technique for the manufacture of nickel superalloy IN617

Spray forming produces cast microstructures with comparatively low macro‐ and micro‐structural chemical segregation and is thus well‐suited for the manufacture of complex chemistry, multi‐component alloys that otherwise show strong elemental segregation. Although spray formed Ni superalloys have shown properties equivalent or superior to their conventionally cast/wrought counterparts, they have not been adopted commercially because of the difficulties in ensuring a high process yield and the complexity and associated cost of large‐scale Ni superalloy melting. In this paper, we describe a hybrid arc spray forming (HASF) process in which costly, large‐scale alloy melting as pre‐cursor to spray forming is avoided by the use of a consumable wire feedstock. To achieve thermal conditions of melt spray forming – essential to produce a refined, polygonal grain structure – a customised secondary atomisation system has been developed. Fe‐0.8 wt%C and Ni superalloy IN617 microstructures and preliminary mechanical properties suggested that hybrid arc spray forming may offer an attractive combination of convenience, low cost and mechanical performance.