A STUDY ON ALUMINIDE COATINGS ON TiAl ALLOYS BY PACK CEMENTATION METHOD

1. IntroductionIntermetallic compound TiAl is expected to be one of the candidates for high temperature systems such as aircraft engines because it has a high specific strength at elevatedtemperatures[1,2]. However, there are two major drawbacks with intermetallic compoundTiAl as an engineering material: one is its poor room temperature ductility and the otheris the poor oxidation resistance above 800xi. The former has been generally overcomeby modification of the microstructure using ternar…     

Development and application of titanium alloy casting technology in China

1 Introduction Titanium, which is named as the third metal after iron and aluminum, is an idea structure alloy for aerospace because of its unique properties such as high specific strength and high corrosion resistance [1-4].Using titanium alloy products, the weight of aerocraft can be greatly lightened and the performance of flight can be dramatically improved. In recent years titanium alloys are not only used widely in aerocraft but also in other industries in the world [6-9]. Due to its hig…     

Thermodynamic calculation of intermetallic compounds in AZ91 alloy containing calcium

1 Introduction Magnesium alloy is regarded as a promising structural material in the 21 century because of its excellent properties such as low density, high specific strength, good castability and machinability[1?5]. The common magnesium alloy AZ91 is, however, unsuitable for using at the temperatures above 120 ℃ because of its poor creep resistance and strength at elevated temperatures[2]. Adding other elements, like calcium, is an important method to improve the mechanical properties of A…     

Recent developments in engineering γ—TiAl intermetallics

γ-TiAl based alloys are rapidly being developed for elevated temperature applications,due to their high strength,light mass and good oxidation resistance.However,th disadvantages of TiAl based alloys are low ductility and toughness at room temperature,and poor workability.Grain refinement is one of the most effective ways for improving room temperature tensile properties and hot workability of ordered TiAl based alloys.At present,the majority of research works have focused on alloy modifications through compositional controls,alloying additions,thermo-mechanical processing and production techniques.This article discusses the research status of TiAl based alloys in the aras of microstructure,alloying,processing and applications.     

Wear resistance and corrosion resistance of VCp particle reinforced stainless steel composites

1INTRODUCTIONRecently,the Fe-base composites prepared byin-situ reaction casting have attracted great inter-est[1,2].This technique is characterized to use thehigh temperature of the ferroalloy melt and pro-mote the chemical reaction between the carbon andalloying elements in the melt,then one or severalceramic particles with high strength and elasticmodulus will be generated[3,4].The amount anddistribution of the ceramic particles,such as TiC,WC,Cr7C3and VC,can be controlled by adjust…     

Ceramic Conversion Treatment of Titanium Aluminide for Improved Tribological Properties

GAMMA based titanium aluminides have greatpotential for high temperature applications,such as jetengine components and exhaust valves in car engines,owing to their high specific strength,high stiffness andgood creep resistance at elevated temperatures[1,2,3].For some of the proposed applications,e.g.,valves in acar engine involving tribo-contact,tribologicalproperties could be thus one of the crucial factors indetermining the life and performance of a titaniumaluminide part.A few studies have…     

YNi_5 PHASE AND ITS EFFECT UPON PROPERTIES OF Ni_3Al ALLOY

An additive of Y to Ni_3Al based alloy may form a phase YNi_5 which increases in amount withthe increase of Y content.It was found that the YNi_5 phase in Ni_3Al alloy could remarkablymake its grains finer and its grain boundaries more crooked other than straight.If the Y con-tent≥0.1 wt-%,it occurs as solid solution state and is favorable to high temperaturecompressive properties and oxidation resistance of the alloy.While Y≥0.3 wt-%,the forma-tion of YNi_5 is predominant in the shape of irregular strips inside Ni_3Al grains and alongtheir grain boundaries.This seems to be quite harmful to high temperature strength,ductilityand oxidation resistance of the alloy.     

INTRODUCTION TO INCONELEL ALLOY 740： AN ALLOY DESIGNED FOR SUPERHEATER TUBING IN COAL-FIRED ULTRA SUPERCRITICAL BOILERS

Chinese utilities as well as those worldwide are facing increased demand for additional electricity, reduced plant emissions and greater efficiency. To meet this challenge will require increasing boiler temperature, pressure and coal ash corrosion resistance of the materials of boiler construction of future coal-fired boilers. A new nickel-based tube alloy, INCONEL^R alloy 740, is described aiming at meeting this challenge. Emphasis will be on describing the alloy＇ s mechanical properties, coal-ash and steam corrosion resistance. Microstructural stability as a function of temperature and time is addressed as well as some of the early methodology em- ployed to arrive at the current chemical composition.     

Thermal activation approaches to deformation mechanisms for high Nb containing TiAl base alloys

The deformation mechanisms in a wide temperature rnage from room temperature to 1200K were investigated by thermal activation approach.Using observed instantaneous stress response to the strain rate jump (Δσtr),the activation volume Vs,then the activation enthalpy ΔH,activation free enthalpy ΔG and activation entropy ΔS were calculated.The apparent activation energy of high temperature deformation is estimated to be 3.66eV,which is larger than the self-diffusion coefficient of binary TiAl(3.01eV).The dislocations at 1173K are generally curved or bowed,even helical-shaped dislocations.The climb of ordinary dislocations as well as twinning has grealty contributed to the plastic deformation.The CRSS at 1173K is estimated to be 180MPa.The higher resisting stress at both room temperature and elevated temperature might relate to the high Nb content of the alloy.     

HIGH TEMPERATURE DEFORMATION BEHAVIOR OF TiAl INTERMETALLIC COMPOUND

The behavior of TiAl interrnetallic compound of Ll_0 type under compressive deformation athigh temperatures and its recrystallization microstructure have been studied.The compressiveproof stress of the polycrystalline TiAl was found to be positive temperature dependence assame as the single crystai one.The correlation of the flow stress together with strain rate anddeformation temperature is in good agreement with the expression:ε=Aσ_p~nexp(-Q/RT)Adjusting the deformation temperature and strain rate to a decrease in flow stress of alloydown to below its brittle fracture stress may improve successfully not only the hot working ofthe TiAl-base alloy but also the fineness of the recrystallized grains.     

Solidification microstructure of centrifugally cast Inconel 625

Centrifugal casting is a foundry process allowing the production of near net-shaped axially symmetrical components.The present study focuses on the microstructural characterization of centrifugally cast alloys featuring different chemical compositions for the construction of spheres applied in valves made of alloy IN625 for operation at high pressure.Control of the solidification microstructure is needed to assure the reliability of the castings.Actually,a Ni-base superalloy such as this one should have an outstanding combination of mechanical properties,high temperature stability and corrosion resistance.Alloys such as IN625 are characterised by a large amount of alloying elements and a wide solidification range,so they can be affected by micro-porosity defects,related to the shrinkage difference between the matrix and the secondary reinforcing phases (Nb-rich carbides and Laves phase).In this study,the microstructure characterization was performed as a function of the applied heat treatments and it was coupled with a calorimetric analysis in order to understand the mechanism ruling the formation of micro-porosities that can assure alloy soundness.The obtained results show that the presence of micro-porosities is governed by morphology and by the size of the secondary phases,and the presence of the observed secondary phases is detrimental to corrosion resistance.     

Environmental corrosion resistance of porous TiAl intermetallic compounds

Porous TiAl intermetallic compound, as a novel substitute for current inorganic porous material, offsets the shortages of both ceramics and metals. The environmental corrosion resistance of porous TiAl intermetallic compound was investigated. The kinetic equation for the cyclic oxidation of porous TiAl alloy at 600 ℃ is determined to be Δm2=1.08×10-5t. After total oxidation of 140 h, porous TiAl intermetallic compound shows more stability of pore structure and the mass gain of TiAl alloy is 0.042 g/m2, which is only 10.6% that of porous 316L stainless steel. The kinetic equation for the cyclic corrosion behavior of porous TiAl alloy in hydrochloric acid with pH=2 at 90 ℃ is determined to be Δm2=5.41×10-5t-2.08×10-4. After 50 h exposure, the mass loss of TiAl alloy is 0.049 g/m2, which is only 14.8% and 5.57% that of porous Ti and stainless steel, respectively. The kinetic equation in hydrochloric acid with pH=3 is determined to be Δm2=2.63×10-6t-3.72×10-6.     

THE STRESS-STRAIN-RESISTANCE RELATIONS IN Fe-Mn-Si ALLOYS

1. IntroductionThe strain sensitivity coefficients of resistance, K, have a value of about 2.0 in elasticregion for most alloys, such as constantan (a Cu-Ni alloy), karma (a Ni--Cr based alloy)and Fe-Cr-Al alloy, except Pt-W alloys. The K values are also about 2.0 in plastic regionfor the most alloys. For the ac--Fe--Mn-Al-Cr alloy it is also about 2.0 during plastic transformation, however, it becomes as high as 4.0--4.8 due to the antiferromagnetic transitionbelow the N6el temperature,…     

Relationship among forging technology, structure and properties of TC21 alloy bars

1INTRODUCTIONNew alloys have been developed for variousdemands[1].Advanced titanium alloy with highstrength and toughness is one of the i mportant de-velopment directions in the related area[2].TC21titaniumalloy is a new(α+β)high strength andtoughness alloy that belongs to Ti-Al-Sn-Zr-Mo-Cr-Nb-Si system.This alloy was patented inChina[3],and quite promising for the structuralparts of advanced aircraft.Several papers describedits characteristics recently[46].Though forgingtechniques…     

Corrosion resistance of electroplated Zn-Co alloy coating

By the NSS test and the test in SO2 gas atmosphere and detecting the φcorr-t curves, Rp-t curves and the cyclic voltammogram curves, the corrosion resistance of the electroplated Zn-Co alloy coating was studied. The corrosion resistance of the electroplated Zn-Co alloy coating is three times higher than that of the galvanized coating. Because the corrosion resistance of the Zn-Co alloy coating is especially remarkable in SO2 gas atmosphere, it is particularly fit to be used as a protective coating in industrial atmosphere. The reason why the Zn-Co alloy coating has such a high corrosion resistance is that its corrosive product has a comparatively great role in depressing the corrosive process.     

MICROSTRUCTURE AND TENSILE PROPERTIES OF Fe3Al-BASED ALLOYS WITH VC AND TiC ADDITIONS

1. Introduction Fe3 Al intermetallics based alloys offer many advantages for various types of structural applications, such as high specific strength, excellent oxidation and sulfidation resistance, and low material cost. However, a lack of ductility at ambient temperature and low strength above 6000C have limited their use as structural materials[13]. Recent research and de- velopment have indicated that the elevated temperature strength and creep resistance can be improved by introducing c…     

EFFECTS OF COMBINED ADDITIONS OF TUNGSTEN AND MOLYBDENUM ON THE CREEP PROPERLIES OF Fe_3Al-BASED ALLOYS

1. IntroductionIron aluminides based on Fe3AI have been interested since the 1930's when their excellent oxidation resistance was first .oted[1'2]. However, poor high--temperature creepresistance is one.of major deterrents to their development as structural materials. Recentdevelopmental efforts have indicated that the creep resistance can be improved by alloyingprocesses, and the effect of some elements such as Cr, Mo, W, Nb, or Zr on the creep resistance of Fe3AI has been investigated re…     

Study on the property of AI-Sn-Pb and its bush material clad with steel strip by liquid-solid bond rolling

1. IntroductionBabbitt alloy, copper-lead alloy, aluminum-tin alloyand aluminum-lead alloy are well known bush materials[1-6].As the progress in automobile industry, there arises a bigdemand of high speed and long life bush materials. A newbush material AlSn8Pb2Si2.5Cu0.8Cr0.2 (ASP) was developedto satisfy the demand in America [7]. This material hasmany advantages, such as good antifriction behavior, highstrength, high wear resistance, good friction consistencyand high load-bearing abilit…     

The in-situ Ti alloying of aluminum alloys and its application in A356 alloys

1. Introduction Titanium is one of the most effective grain refinement elements of aluminum alloys. The grain of aluminum alloys can be effectively refined if containing up to 0.2% titanium, which results in improvement of mechanical properties and performance [1-8]. Titanium is usually added into aluminum melt by melting Al-Ti or Al-Ti-B (Ti/B= 5:1) master alloy. This requires strict control in melting temperature and holding time, resulting in the complicacy to control the quality of allo…     

Effects of can parameters on canned—forging process of TiAl base alloy（I）——Microstructural analyses

By using thermal simulation technique,.the conventional canned-forging process of TiAl based alloy was studied.The effect of can parameters on the microstructures of TiAl alloy was analyzed in this process.The results show that,the deformation microstructure of TiAl based alloy without canning is inhomogeneous.In lateral area,crack and shearing lines can be found;while in central area,fine-grained shearing zone can be found.The effect of can is to reduce the secondary tensile stress.However,only when the deformation of the steel can is coincidental with that of TiAl alloy ingot,can this effect be effective.Moreover,a thick can would enhance the microstructural homogeneity in TiAl based alloy.With the H/D ratio of the ingot increasing.the deformation of TiAl alloy would be more unsteady,therefore,a thicker can should be needed.