Thermal Fatigue Properties Research Articles

THERMAL FATIGUE CRACK INITIATION AND PROPAGATION OF MULTIELEMENT Al-7.5Si-4Cu ALLOY

With the rapid development of automotive industry,the requirements for engine performance has become increasingly higher and higher,such as dynamic performance,environmental performance,fuel economy performance and so on.Obviously,using lighter aluminum engine has become the future of the automobile industry.When start or stop the engine,the engine generates drastic temperature field that will make parts of the engine components into the plastic deformation zone.If the engine components continue like this,extremely high thermal strain will cause the thermal fatigue failure of aluminum alloy for automotive engine.Thermal fatigue is a more serious form of material fatigue failure.The thermal fatigue is prevalent in many important engine castings,such as cylinder body,cylinder head,piston and so on.Therefore,study on thermal fatigue properties of multivariate Al-Si-Cu cast alloy has the most important significance.Based on this thermal fatigue behaviors of multivariate Al-7.5Si-4Cu alloys under different heat treatment were investigated in the temperature ranges of room temperature to 350℃.The thermal fatigue cracks of the tested specimens were observed using OM and SEM.The results demonstrate that thermal fatigue properties of the alloy after T6 heat treatment is better than the alloy after cast-quenching+aging heat treatment and the cast alloy.Reasonable heat treatment process can improve the strength,the plasticity and the thermal fatigue property of multivariate Al-7.5Si-4Cu alloy,including reduce the rate of crack propagation. The main reason of crack initiation is oxidative microstructure induced by thermal stress.Fatigue crack expands along the grain boundary by passivation-sharpen of crack tip in the early.In the late,fatigue crack expands with both intergranular way and transgranular way by passivation-sharpen of crack tip and siamesed holes on front edge of crack tip.The Si phases can affect fatigue crack propagation.When the angle between the fatigue crack propagation and the short axis of the Si phase is more than 60°,fatigue crack expands asbypass-wall expansion.When the angle between the fatigue crack propagation and the long axis of the Si phase is more than 60°,fatigue crack expands asthrough-wall expansion.Oxidation behavior effects significantly at the crack initiation period.After T6 heat treatment,the antioxidant property of multivariate Al-7.5Si-4Cu alloy is the best.Oxidation kinetics curves of multivariate Al-7.5Si-4Cu alloy under the different heat treatment are all logarithmic relationship.

Study on the Thermal Fatigue and Anti-Melting Loss Properties of the H13 Steels with Surface Vapor Oxidation

H13 steel specimens with vapor oxidation surface treatment and without surface treatment, were carried out by thermal fatigue test and melting-loss test to research the effect of vapor oxidation surface treatment in the aluminum alloy die casting. The results show that the vapor-oxidized specimens have better erosion resistance and similar thermal fatigue resistance to those without surface treatment. Compound layer and compact layer form in melting-loss test are mainly Fe2Si2Al8 and Fe2Al5, respectively.

Properties of SnZn lead free solders bearing rare earth Y

Rare earth (RE) Y has been incorporated into eutectic SnZn solders to study the wettability, mechanical properties, oxidation resistance, microstructures and thermal fatigue behaviours. The results indicate that adding trace amount of RE Y can remarkably improve the wettability of SnZn solders. When the content of RE Y is 0·06 wt-%, the tensile and shear forces of SnZn-xY solder joints give 24·1% and 27·2% increase after soldering. In addition, it is found that SnZn0·06Y has better oxidation resistance than that of SnZn solder, and the microstructures of SnZn solders can be refined by the addition of RE Y; the size of Zn rich phase can be reduced obviously. Moreover, SnZn0·06Y shows superior thermal fatigue property over SnZn solders. It can be concluded that the optimum content of RE Y is 0·06 wt-% for SnZn solders.

Study on the Influence of High Temperature Homogenizing and Solution on the Microstructure and Property of 4Cr5MoSiV1 Steel

4Cr5MoSiV1 steel, a widely used for hot work mould, contains Cr, Mo, V alloying elements that easily form carbides. The Micro-area chemical composition, microstructure, impact toughness and thermal fatigue behavior of 4Cr5MoSiV1 and 4Cr5MoSiV1H steels were investigated, the latter was carried on high temperature homogenizing and solution based on the former. The results showed that bulk eutectic carbides and elements segregation contained in the 4Cr5MoSiV1 steel reduced the impact toughness. But the impact toughness of the core of the mould steel block and thermal fatigue property of 4Cr5MoSiV1H steel were improved because the elements segregation and eutectic carbides was eliminated through the high temperature homogenizing and solution.

Effects of alloying elements on the thermal fatigue properties of the 15 wt% Cr ferritic stainless steel weld HAZ

We investigated the effects of Nb, W, and V alloying elements on the thermal fatigue properties of the ferritic stainless steel weld heat affected zone (HAZ). Simulation of the weld HAZ and thermal fatigue testing were carried out using a metal thermal cycle simulator (MTCS) under a complete constraint force in the static jig. The fatigue life during cyclic heating and cooling in the temperature range of 200–900°C was strongly related not only to precipitation and coarsening of MX type and Laves precipitates, but also to the Nb content in the solid solution and grain coarsening. The thermal fatigue life increased with Nb and W contents due to the increased amount of (Nb,Ti)(C,N) precipitates and a less coarsened Laves phase, respectively. Contrary to the results with Nb and W additions, there were no obvious effects of V addition.

Thermal fatigue properties of differently constructed functionally graded materials aimed for refurbishing of pressure-die-casting dies

Different surface layers, constructed on the basis of functionally graded materials using a laser cladding technique, were designed to study the possibility of using them in applications subjected to thermal fatigue. Three different filler materials, varying in terms of the concentrations of alloying elements were used. A graded chemical composition was achieved, varying the concentration of silicon from 0.1wt.% at surface layer to 1wt.% in the base material. A specially designed thermal fatigue test was utilized for the assessment of the thermal fatigue resistance of designed surface layers and compared with base tool steel AISI H13. The results of thermal fatigue testing showed that the different concentrations of alloying elements in the surface layers resulted in different thermal fatigue resistances. The thermal fatigue resistance was observed to be approximately 27times higher in specimens with lower silicon content compared to base material. This was found to be closely correlated with the microhardness and the resistance to softening during annealing.

The effect of the precipitates type on the thermal fatigue properties of 18% Cr ferritic stainless steel weld HAZ

Abstract The microstructural changes and precipitation behavior during thermal fatigue testing of the 18% Cr ferritic stainless steel weld heat affected zone (HAZ) were investigated. The simulation of the weld HAZ and thermal fatigue testing were carried out using a metal thermal cycle simulator (MTCS) under a complete constraint force in the static jig. The thermal fatigue properties of the weld HAZ deteriorated during cyclic heating and cooling in the temperature range of 200–900 °C due to the decrease of Nb content in the solid solution, coarsening of MC type precipitates, the Laves phase, and M6C precipitates with grain coarsening and softening of the matrix. Primary and secondary fatigue cracks were initiated from the notch of the specimen after around 60% of the total number of cycles due to the coarsened particles and grain boundary oxidation. As the number of fatigue cycles increased, a transgranular crack propagated towards the center of the specimen and finally the fracture was complete as it merged with the spontaneously formed and coarsened cavities in the specimen during the thermal cycling.

Effect of Zn on properties and microstructure of SnAgCu alloy

The microstructures, wettabilities and mechanical properties of SnAgCu-xZn (x = 0, 0.5, 0.8, 1.0, 1.2, 2.0, 2.5, 3.0) solders were investigated, respectively. The results indicated that adding small amount of Zn can evidently improve the wettability, mechanical properties and refine the microstructure of SnAgCu lead-free solder. However, there existed an effective range for the Zn addition, the best Zn content was found to be 0.8 % in the current study. Moreover, the presence of Zn in the solders plays a major role in inhibiting the growth of Cu–Sn intermetallic layer in the solder/Cu interface. Based on thermal-cycling tests, it is demonstrated that the addition of Zn can enhance the thermal-fatigue properties of SnAgCu solder joints.

The Influential Factors Analysis of Surface Crack Propagation Behavior of ZrB2-20%SiC-10%AlN Ceramic Subjected to Thermal Shock

The indentation-quench method for investigating surface crack propagation has been studied through both experiments and model. The influential factors for surface crack propagation such as specimen thickness, thermal fatigue property, and quench temperature difference (ΔT) and one single specimen being used throughout a whole test ΔTwere surveyed in this paper. Practical results were obtained for ZrB2-20%SiC-10%AlN (ZSA) ultra-high temperature ceramic. The percentage crack growth versus ΔTcurves showed stable crack growth in a relative low ΔTinterval and unstable crack growth above a certain ΔT, and these regimes were sensitive to the thickness. The total stress intensity factor (KI) combining residual stress and thermal stress considering dynamical behavior during the quenching test was calculated by a surface crack theoretical model, the result of calculation was analyzed influential factors and crack propagation .

Failure characteristics and life prediction for thermally cycled thermal barrier coatings

The effect of high temperature hold time at 1050°C on thermal fatigue properties and failure characteristics of electron beam-physical vapor deposited (EB-PVD) thermal barrier coated samples (TBCs) was investigated in this work. To clarify this effect, the microstructure, especially that near the interface after certain thermal cycles was characterized by scanning electron microscopy (SEM). Results revealed that with increasing hold time at high temperature, fatigue life first increased then decreased and the failure mode diverted from the interfacial failure mode to one that consisted of both the interfacial failure mode and failure within the TBC. Failure was determined by strain energy density in the ceramic coating and the TGO, the fracture toughness of the ceramic coating, the TGO and the interface, and their correlations with microstructure defects near the interface. Based on analysis of the failure mechanism and the microstructure evolution near the interface, and by combining the simulation modeling of the thermal cycling response, a damage accumulation life prediction model was developed in terms of the TGO thickness. This model, which considered the evolution of the fatigue stress due to the increase in TGO thickness, was able to predict thermal fatigue life of the TBCs/nickel based superalloy system under different thermal cycling histories.

Thermal fatigue behavior of direct metal deposited H13 tool steel coating on copper alloy substrate

Thermal fatigue performance of direct metal deposited H13 tool steel coating on copper alloy substrate was investigated for high pressure die casting applications. An innovative thermal fatigue test rig was used which is capable of applying cyclic identical energy on the test materials regardless of thermal conductivity property. H13 tool steel was coated on cylindrical copper alloy core material both directly as well as using 316 stainless steel as a buffer layer to evaluate and compare their thermal fatigue properties. Two types of cracks at the surface of both coatings were observed and investigated. The network of small and shallow cracks on the surface was the result of thermal stress while the large catastrophic cracks were believed to be the consequence of thermal stress coupled with the thermal expansion mismatch between the H13 tool steel coating and copper alloy core materials. The H13 tool steel, coated with 316 stainless steel showed much less number of cracks compared to the directly coated H13 tool steel indicating superior thermal fatigue resistance. Moreover the first layer of the directly coated H13 tool steel showed vulnerable behavior under high temperature application showing numerous cracks. Both coatings showed no crack propagation along the interface between coatings and the substrate materials.

The Thermal Fatigue Performance for Cast Iron Brake Drum of Large Trucks

This paper studies the application in different cast iron brake drum the thermal fatigue properties of materials. The results show that the stress concentration factor of grey cast iron, hot fatigue crack initiation, low intensity, and easy to expand, organization crack initiation poor stability, antioxidant ability is poor, thermal fatigue is poorer. 35% of vermicular cast iron and of ductile iron high strength, toughness, good stress concentration factor small, thermal fatigue is well.

Thermal Shock Cracks Initiation and Propagation of WCp / Steel Substrate Surface Composite at 500°C

In order to provide a theoretical basis for the study of thermal fatigue properties on surface composites, thermal shock cracks initiation and propagation of WCP reinforced high chromium steel substrate surface composites were studied by thermal shock test method at 500 °C. The results show that cracks initiation and propagation begin within a few thermal shock cycles, and after 15 thermal shock cycles, the composites remain intact, indicating a good thermal shock resistance. The thermal shock cracks consist mainly of longitudinal and transverse cracks. Within a few thermal shock cycles, the initiation and propagation of longitudinal cracks play a dominant role; however, with the increase in the number of thermal shock, the transverse cracks may play a key role as the length and number of both types of cracks increases. However, the increase is slow. The longitudinal cracks are mainly caused by the first class thermal stress and the transverse cracks result from the culminant effects of the first and second thermal stress, interacting with each other.

High heat load properties of actively cooled W/CuCrZr mock-ups by diffusion bonding with Ni or Ti interlayer

Two actively cooled mock-ups with 5 mm thick tungsten armor, joined to CuCrZr alloy, were successfully developed by diffusion bonding technique with Ti or Ni interlayer for the EAST device in ASIPP. Its thermal response and thermal fatigue properties were investigated with active cooling. No cracks and voids occurred at the interface of W/CuCrZr after thermal response test with a heat flux from 0 MW/m 2 to 10 MW/m 2. It survived up to 200 cycles under 10 MW/m 2. The temperature distributions of the mock-up were estimated by Finite Element Analysis. The simulation results indicated that thermal contact capability between the tungsten and the copper alloy with Ti interlayer was higher than that of Ni interlayer. Results showed that diffusion bonding of W/CuCrZr with Ni or Ti interlayer is a potential candidate for a high heat resistance armor material on plasma facing components (PFC).

Heat Resistance of Ferritic Stainless Steels with 15% Chromium for Automobile Exhaust System

The high-temperature strength and thermal fatigue properties of Fe-Cr-Nb-Mo ferritic stainless steel (FSSNEW) developed for automobile exhaust system were investigated. The results show that the high-temperature tensile strength and yield strength of FSSNEW are better than or equal to those of the presently applied ferritic stainless steels. The thermal fatigue cracks nucleate at the V-notch. The inclusions along grain boundaries become prior regions for initiation of the cracks. The inclusions distributed at the defects make the formation of cracks in the materials easily through the effects of cycle thermal stress and thermal strain. The length and propagated rate of thermal fatigue cracks increase with the maximum tested temperature increasing. When the maximum temperature arrives at 900°C, the high-temperature oxidation is serious along the grain boundaries, which aggravates the cracks propagating along the grain boundaries. The principle mechanism of stress assisted grain boundary oxygen (SAGBO) embrittlement can be applied to illustrate the effects of external stress on aggravating the damage caused by environmental factors. Therefore, the high-temperature oxidation is the main reason for the propagation of thermal fatigue cracks. The FSSNEW is satisfied for the applied requirement of high-temperature strength in the hot side of the automobile exhaust system.

Influence of direction of notch on thermal fatigue property of a directionally solidified nickel base superalloy

Thermal fatigue property of a directionally solidified nickel base superalloy at the condition of different notched orientation and upper temperatures was investigated. The results show that cycle numbers of crack initiation decrease, propagation rate of crack increases and resistance of thermal fatigue reduces with the rise of upper temperature. Thermal fatigue property of the specimen with the notched direction vertical to orientation of dendrite growth (DZ319T) is superior to that of the specimen with the notched direction parallel to orientation of dendrite growth (DZ319L). DZ319L alloy initiates thermal fatigue crack by carbide and propagates along the direction of carbide distribution, which resultes in big propagation rate and poor thermal fatigue property. Crack initiation of DZ319T alloy is mainly by oxidized cavity. The join of oxidized cavity makes crack propagate. There are two cracks in DZ319T alloy, which greatly drops the stress concentration near the notch and decreases the propagation rate of crack. DZ319T alloy has excellent thermal fatigue property.

Study on the Thermal Fatigue Resistance of Cr17Mn10Ni3 Heat-Resistant Steel

In order to prolong the life of inner liner of coke can, the thermal fatigue property of Cr17Mn10Ni3 heat-resisting steel was analyzed and studied from cast metallurgical structure, the morphology of crack surface and cross-section, the injury factor by OM, SEM, photoshop and imagetool software. The results shows, Cr17Mn10Ni3 has a good thermal fatigue property because of the microstructure with good thermal conductivity, austenite matrix and break carbide lying in treelike crystals. It decreases the innerstress and postpones the time of crack formation and extension, during the process with 1100°C and room- temperature water cooling. The cracks mainly appear in the phase interfaces between carbides and matrix, ferrite and austenite, and grain boundaries. The thin and deep cracks with high concentration are beneficial to relax the elastic strain energy. But a single and thick crack easily widens and deepens to be detrimental to the thermal fatigue property.

High heat load properties of actively cooled W/CuCrZr mock-ups by cladding and diffusion bonding with a two-step process

The surface of W was grooved into an arc wave surface, on which a Cu layer was then clad at 1150–1200 °C to form a pre-joining clad sample. The clad sample was then diffusion bonded to a CuCrZr at 450 °C to form an actively cooled mock-up. The thermal response and thermal fatigue properties were investigated by active cooling technology. The results showed that no cracks and voids occurred at the interface of W/CuCrZr mock-ups after thermal response test with a heat flux from 0 to 10 MW/m 2, which survived up to 200 cycles under 10 MW/m 2. The residual stresses of the mock-up were estimated by Finite Element Analysis. The simulation results indicated that the residual stresses were more beneficial to crack arrest for the mock-up using an arc wave interface instead of a flat interface. This technique provides an available method of bonding W to CuCrZr.

J031044 熱疲労によるセラミックス基板の強度低下に関する研究([J03104]電子情報機器,電子デバイスの強度・信頼性評価と熱制御(4))

In order to establish evaluation method of thermal fatigue property on ceramic substrate, thermal cycle fatigue test and 4 point bending test were carried out using specimens of Cu/Al203. As the results, the ratio of residual strength P/Po has decreased with increasing thermal cycles. The cracks were generated on the ceramic at about corner of metal plate. Next, in order to investigate the residual stress distribution of ceramics caused by junction between ceramics and metal plate and the stress distribution of ceramics caused by thermal fatigue, FEM was carried out. As the results, it has been understood that the tensile residual stress on ceramics at about corner of metal plate is generated by the junction process and that the repetition of the tensile stress and compressive stress on ceramics at about corner of metal plate are occurred by the thermal cycles.

Effect of Thermal Cycling on Properties and Microstructure of SnAgCuCe Soldered Joints in QFP Devices

Increasing global concern about the environment is bringing regulatory (European directives) and consumer ("green products") pressure on the electronics industry in Europe and Japan to reduce or completely eliminate the use of lead (Pb) in products. Among all lead-free solder alloys, SnAgCu solder system, which has better thermo-mechanical properties compared with those of SnPb solder, is proven to be one of the promising candidates for electronic assembly. Previous work also revealed that adding a small amount of rare earth Ce into SnAgCu solder can visibly improve the properties and inhibit the excessive growth of the intermetallic compound layer. Thermal fatigue properties of SnAgCuCe soldered joints in QFP devices under thermal conditions have been investigated by finite element method and experiments. Based on creep model of low stress and high stress, corresponding creep subroutine was established for simulating the stress and strain response of SnAgCuCe soldered joint from -55 ℃ to 125 ℃, and fatigue life was calculated using creep fatigue life prediction equation. Moreover, thermal cycling experiments were conducted, the experimental results were found to be close to the simulated results. In addition, the tensile force of SnAgCuCe soldered joints decreased with increasing number of thermal cycles, and the fracture mechanism transformed from toughness fracture to brittle intergranular fracture. Moreover the tensile force changes and fracture microstructure evolution could benefit the quantitative evaluations of the mechanical performances of lead-free soldered joints under thermal cycling loadings.