Thermal Fatigue Properties Research Articles

Characterization of thermal fatigue properties of lead-free Sn–Cu–Al–Mg solder alloy produced by powder metallurgy method

In the present study, lead-free Sn–Cu–Al–Mg-based solder alloys for electronics packaging were produced. Effects of thermal shock and thermal stress on the crack formation in the Sn-based solder alloys were investigated. Lead-free quaternary Sn–Cu–Al–Mg-based solder alloys were produced by using mechanical alloying and powder metallurgy route. Soldering involves using a molten filler metal to wet the surfaces of a joint. Wave soldering is a method for mass assembly of printed circuit boards involving through holes, surface. Lead-free solder alloys must show high wettability, suitable mechanical properties, electrical conductivity, high electrochemical corrosion resistance, and low cost. Mechanical alloying and powder metallurgy method were used in order to prevent formation of intermetallics and formation of voids. Mechanical alloying–powder metallurgy method could reduce the micro/macro-segregation and provide homogeneous microstructure. Initially, elemental metal powders were mechanically alloyed in a ball mill by using zirconia balls in order to produce alloy powders. Then, the alloy powders were compacted at 300 MPa and then the green specimens were sintered at 180 °C for 60 min. Nondestructive ultrasonic tests and eddy current tests were used for characterization of the solder alloy specimens. Elastic modulus of the Sn alloys was determined by ultrasonic measurements. Electrical conductivity of the specimens was determined by using eddy current tests. Microstructure was studied by scanning electron microscope. Effects of thermal shock and thermal stress on the crack formation in the alloys were investigated by heat treatment cycles in a chamber furnace. Heating cycles for thermal stress consist of heating to 150 °C and slow cooling. Heating cycles for the thermal shock consist of heating and quenching. In addition, electrochemical corrosion behaviour of the Sn solder alloys was investigated in NaCl solution.

Performance of rubber modified asphalt mixture with tire-derived aggregate subgrade

The objective of this research is to investigate the long-term performance of rubber-modified asphalt mixture (RMA) on Tire-Derived Aggregate (TDA)-replaced saturated subgrade as a drainage material. In lab testing setup, the mixtures were subjected to a 5-day conditioning at 85°C to ensure complete long-term aging. A series of laboratory and field tests were conducted. The study found that the surface course rubber mix had the best-cracking resistance than the leveling course control mix and surface layer control mix. Additionally, the fracture energy of the surface layer rubber mix was 17.4–21.9 % higher than that of the surface layer control mix. After the long-term aging condition, all three types of hot mix asphalt (HMA) exhibited exceptional resistance to deformation. Rubber-modified asphalt improved fatigue properties and crack performance. In summary, implementing RMA in pavement construction improved the pavement's thermal cracking and fatigue properties and significantly reduced pavement noise. TDA has potential as a fill material in subgrade applications, and rubber-modified asphalt shows promising performance for asphalt pavement.

Unveiling the enhancement of thermal fatigue properties of FeCrB alloy induced by in-situ particles

In order to overcome the inferior thermal fatigue (TF) properties of FeCrB alloy, FeCrBTi alloy containing in-situ formed particles has been developed. This study systematically investigated the enhancement mechanism induced by in-situ particles through the TF experiment. Results demonstrated in-situ particles not only directly alter the crack propagation path but also refine the microstructure, thereby contributing to stress reduction and improving mechanical properties. Furthermore, in-situ particles promote the formation of a compact and adhesive oxide scale. Therefore, the TF properties of FeCrBTi alloy are 3.1 times higher compared to FeCrB alloy. This research shed a novel light on the improvement of TF resistance of tool steels.

A new type of high thermal shock resistance tool for inhibiting thermal crack

Due to the periodic alternation of hot and cold in the cutting process, cutting tools often fail owing to thermal cracks, making it difficult to intermittently cutting materials. Therefore, in order to suppress the initiation of thermal cracks in cutting tools, a new type of high thermal shock resistance oblique gradient cutting tool (marked as TDZ-X) has been fabricated. The material system of the cutting tool is designed by the temperature field model of the cutting tool. The direction angle of TDZ-X is accurately designed based on the thermal crack initiation area of the tool. A new method for studying the thermal fatigue properties of tool materials is proposed, the tool is heated by ultra-fast picosecond laser to simulate the thermal shock in the milling process. The thermal fatigue resistance and the thermal shock resistance of TDZ-X, the gradient tool and the homogeneous tool are compared and studied, the results show those of TDZ-X are best than those of the other two tool materials. Through the design of TDZ-X, the thermal shock resistance of the tool material has been significantly improved, and the effectiveness of inhibiting thermal crack initiation has been verified by cutting experiments, which provides a new method for design and fabrication of discontinuous cutting tools with long tool life and high reliability.

High-temperature thermal fatigue of Ni3Al-based single crystal alloy affected by wall thickness and peak temperature

Complex thin-walled structures are commonly employed in turbine components to improve cooling efficiency. However, thin-walled blades are prone to thermal fatigue failure due to the high thermal stress induced by frequent and abrupt temperature fluctuations during duty cycles. The thermal fatigue behavior of Ni3Al-based single crystal alloy with thin-walled structure during 25 °C ↔ 1000 °C/1100 °C was investigated by combining thermal fatigue tests and finite element simulation. The thermal fatigue demonstrated a significant thickness debit effect, with thermal fatigue property dropping as peak temperature and wall thickness increased. Wall thickness had a more pronounced effect than peak temperature. Visible slip traces were found on the wall thickness surface, and their density was positively correlated with wall thickness. Further investigation revealed that thermal fatigue is primarily driven by the octahedral slip system ({111}<110>), with significant contributions from (111)[101‾] and (1‾1‾1)[101]. Simulations of thermal stress distribution and J-integral at the crack tip during crack initiation and propagation stages indicated that wall thickness influences thermal fatigue properties by affecting thermal stress concentration at the notch and crack tip. Higher peak temperatures increased thermal stress and reduced yield strength, thus diminishing thermal fatigue performance. A thermal fatigue crack propagation prediction model was constructed incorporating Paris' law and the J-integral. The model revealed an unfavorable correlation between material Cj/ nj and both peak temperature/wall thickness, indicating that both factors adversely affect thermal fatigue resistance.

Simulation of Thermal Dissipation and Fatigue Properties of a Pressing Sealed Insulated Gate Bipolar Transistor Device

Insulated gate bipolar transistor (IGBT) is widely needed in many applications, such as motors, inverters, express railways, and automobiles. As the integrity level of IGBT increases, thermal management becomes a more significant issue, especially when third-generation semiconductor chips made with SiC or GaN come into application. Here, a press packaging SiC IGBT module is designed, which involves silver sintering. Firstly, we make a thermal analysis using the finite element method (FEM). Then, a heat dissipation plane is optimized. Groups of heat sink materials and airflow velocities are investigated, and an optimized one is chosen as the basis of further fatigue analysis. In the simulated working condition, the maximum temperature can reach 100°C, which could further induce serious problems in fatigue performance. We have analyzed 4 models with different silver layer edge shapes. The best one shows a 27% higher expected fatigue life than the standard one, which shows that the fatigue performance is very sensitive to the edge shape of the silver layer. This research can help further optimization and designing of advanced IGBT devices.

Effects of deep cryogenic treatment on the microstructure evolution, mechanical and thermal fatigue properties of H13 hot work die steel

The service life of hot work die steel is significantly influenced by its microstructure and thermal fatigue properties. This paper explores the impact of deep cryogenic treatment (DCT) on H13 hot work die steel's microstructural evolution and mechanical as well as thermal fatigue properties. The results demonstrate that a portion of unstable retained austenite transforms into martensite during deep cryogenic treatment and numerous finely dispersed carbides precipitate from the matrix, thereby enhancing hardness. Analysis of the average crack length and distribution of thermal fatigue test samples reveals that the average crack length and crack density of DCT-treated samples are lower than those of non-DCT-treated samples. Thermal fatigue cracks in the specimens primarily originated from trigeminal grain boundaries and the carbides are found at the crack tips. DCT facilitates the precipitation of fine and dispersed carbides, imparting a robust pinning effect on boundary migration and thereby impeding the initiation and propagation of thermal fatigue cracks. Furthermore, deep cryogenic treatment results in a reduction in the number of M23C6 type carbides with large particles and an increase in smaller M6C type carbides during the thermal fatigue test. This indicates a positive influence on the carbide distribution and further contributes to the improved thermal fatigue resistance of the hot work die steel.

Frictional Wear and Thermal Fatigue Properties of Die Steel after Ultrasound-Assisted Alloying

The surface layer of 8407 die steel was strengthened using the combination of ultrasonic surface rolling and high-energy ion implanting in the present work. The strengthened layer was then characterized via microstructure observation, composition analysis, and hardness test. After that, the frictional wear and thermal fatigue properties of high-energy ion implanting specimens and composite-reinforced specimens were compared. Results show that the pretreatment of specimens with ultrasonic surface rolling causes grain refinement in the material surface, which promotes the strengthening effect of high-energy ion implanting. The wear volume of composite-reinforced specimens at medium and high frequencies is reduced by about 20%, and the wear resistance of these specimens is significantly improved with a lower friction coefficient and wear volume at moderate and high frequencies in alternating load friction experiments. Meanwhile, the thermal fatigue crack depth of composite-reinforced specimens is reduced by about 47.5%, which effectively prevents the growth of thermal cracks in the surface, thus improving the curing ability of the implanted elements. Therefore, composite strengthening of the mold steel surface is conducive to improving the cycle life, ensuring accuracy, effectively hindering the expansion of thermal cracks, and saving the cost of production.

Microstructure and properties of plasma cladding Ni-based alloy coated on 40Cr Surface

Three Ni-based alloys (Ni60, Ni65, Ni60W) were selected to be coated on the surface of 40Cr and 20 steel. The microstructure, phase composition and elemental distribution of the coatings were characterised respectively to discuss the effects of different substrates, cladding materials, and processes. The corrosion and thermal fatigue behaviour of the coatings were investigated. The results show that the coatings prepared by plasma cladding have a dense microstructure with few defects and a white bright band of a certain thickness was formed between the coating and the substrate. The white bright band between the coating prepared by flame spraying and the substrate was not obvious. The main phase compositions of the coatings are Cr23C6, Cr7C3, Ni2.9Cr0.7Fe0.36 and FeNi3 phases, with the W2C phase also present in the Ni60W coating. The heat-affected zone (HAZ) of the coating is influenced by the coating preparing processes, substrate material and process state of substrates: the size of the HAZ of the plasma cladded coating is smaller than that of the flame sprayed coating, the HAZ of the 40Cr substrate is smaller than that of the 20 steel, and the HAZ of the tempered 40Cr substrate is smaller than that of the annealed 40Cr substrate. The Ni-based alloy coating can effectively improve the surface hardness of the substrate. The Ni65 alloy powder is the most effective (HV0.5992), followed by the Ni60W alloy powder (HV0.5798) and finally the Ni60 alloy powder (HV0.5712). The Ni65 alloy coating has the relatively best thermal fatigue properties, followed by the Ni60W alloy coating and the Ni60 alloy coating is the relatively worst. At the same time, the corrosion resistance of different Ni-based alloy coatings is consistent with the thermal fatigue properties of the coatings.

Thermal Fatigue Crack Propagation Process and Mechanism of Multicomponent Al-7Si-0.3Mg Alloy

The thermal fatigue behavior of multicomponent Al-7Si-0.3Mg alloys in four different treatment states at typical temperature amplitudes 20 °C→350 °C was studied. The morphology of the second phase particles and crack propagation, and distribution characteristics of dislocations in the thermal fatigue specimens of multicomponent Al-7Si-0.3Mg alloys, were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX spectrum), and transmission electron microscopy (TEM). The influencing factors, the process, and the mechanism of thermal fatigue crack propagation were mainly studied. The results show that under the same temperature amplitude, the thermal fatigue properties and dislocation densities of the new aluminum alloy and the new aluminum alloy under T6 heat treatment are significantly higher than that of the multicomponent Al-7Si-0.3Mg alloy in cast and refined and modified treatment. The crack growth of thermal fatigue specimen depends on three factors: the temperature amplitude, oxidation, and residual stress. The process of thermal fatigue crack propagation mainly experiences crack initiation and the formation of microcracks, but only a few microcracks continue to expand rapidly or preferentially expand into main cracks. The mechanism of thermal fatigue crack propagation is mainly under the action of thermal stress, the crack tip undergoes a cycle of repeated alternation of sharpening → passivation → sharpening, and the crack continues to move forward from its tip intermittently in the way of propagation → stopping → propagation until fracture failure.

Thermal fatigue testing with repeatable temperature cycles on thermomechanical simulator

This paper presents two thermal fatigue tests developed to simulate the typical thermal fatigue behavior of hot-work tools and rolls. The tests are carried out on a Gleeble 1500D thermomechanical simulator with computer-controlled heating and cooling of the test specimens. In the first test, internal cooling of the specimens is performed, and in the second test, external cooling is performed. This allows constant test conditions and the collection of reliable experimental data on the thermal fatigue behavior. The internally cooled test rig is used for testing the thermal fatigue properties of bulk materials. Indefinite chill double-poured cast iron is used to present the basic capabilities of the test. At the material, the cracks take flattened graphite–cementite pathways. The external cooling test rig, on the other hand, is designed for comparative testing of four surfaces simultaneously. Thus, the capabilities of the second test are presented in the comparative testing of three different laser-welded functionally graded material surface layers and the basic H13 tool steel, simultaneously. The highest thermal fatigue resistance is shown by the weld with the lowest silicon (Si) content. Quantitative evaluation of thermal fatigue resistance as well as following of degradation processes in both tests is enabled.

A Mini-Review on the Thermal Fatigue Properties of Copper Materials Applied at the Front-End of Synchrotron Radiation Facilities.

Oxygen-free high-conductivity copper (OFHC), chromium-zirconium copper (CuCrZr), and Glidcop® AL-15 are widely used in the high heat load absorber elements at the front end of synchrotron radiation facilities. It is necessary to choose the most suitable material according to the actual engineering conditions (such as the specific heat load, material performance, and costs). In the long-term service period, the absorber elements have to bear hundreds or kilowatts of high heat load and its "load-unload" cyclic loading mode. Therefore, the thermal fatigue and thermal creep properties of the materials are critical and have been extensively studied. In this paper, based on the published pieces of the literature, the thermal fatigue theory, experimental principles, methods, test standards, test types of equipment, and key indicators of the thermal fatigue performance of typical copper metal materials used in the front end of synchrotrons radiation Facilities are reviewed, as well as the relevant studies carried out by the well-known synchrotron radiation institutions. In particular, the fatigue failure criteria for these materials and some effective methods for improving the thermal fatigue resistance performance of the high-heat load components are also presented.

Microstructural Evolution and Tensile Properties of a Corrosion-Resistant Ni-Based Superalloys Used for Industrial Gas Turbines

As an important mechanical property, tensile behavior has been regarded as an indicator for the creep and thermal mechanical fatigue properties of Ni-based superalloys. The tensile property of Ni-based superalloys is closely related to the amount, size, and distribution of γ'-phase and carbides. To further clarify the tensile deformation mechanism of the CM247LC alloy, this study investigated its solidification characteristics and directionally-solidified and heat-treated microstructure. The dependence of tensile properties on the varied temperature ranging between 650 and 950 ℃ is discussed in detail. It was found that the deformation mechanism at 650 ℃ is dominated by the shearing of dislocations into the γ'-precipitates to form the superlattice stacking faults. At 800 ℃, the K-W lock leads to the anomalous yield effects. At 950 ℃, the deformation mechanism is dominated by the dislocations bypassing the γ'-precipiates. The results provide a comprehensive understanding of the CM247LC alloy and are beneficial for the development of corrosion-resistant Ni-based superalloys.

Effect of pre-welding and welding voltage on thermal fatigue property of parallel gap resistance welded joint between Ag interconnector and Au/Ag back electrode of GaAs solar cell

Thermal reliability of Au/Ag interconnection is a crucial factor for the life of solar cell array during service in space. Although it is known that increasing the heat input can effectively improve the joint thermal fatigue resistance, such welding energy increase has to be achieved by coordination of various parameters to avoid damage to the solar cell matrix. Therefore, clarification of specific strengthening mechanism by different welding parameter is significant for the further improvement of joining quality. In this study, parallel gap resistance welding (PGRW) is used to perform micro-leveled interconnection between Au/Ag back electrode of triple-junction GaAs space solar cell and Ag interconnector. Besides the original parameter set, methods of welding voltage increase and pre-welding are used to improve the joining quality. Subsequently, the samples are subjected to temperature cycling environment between−160 °C and+120 °C for various cycles. According to the tensile-shear test results, although both methods have effectively improved the joint thermal fatigue property, quite different strengthening routes are shown. On one hand, joints strengthened by increasing welding voltage have higher tensile shear force than the ones strengthened by pre-welding. On the other hand, joints optimized by pre-welding show much stabler tensile-shear property. Material characterization by transmission electron microscopy (TEM) has explained the different strengthening routes that increase of voltage actually changes the joining mechanism from original solid-phase diffusion between Au/Ag interface into total melting, while pre-welding keeps the interface with partial solid-phase diffusion interface. Besides, electron back scattered diffraction (EBSD) results indicate that the evolution of residual stress concentration is the intrinsic reason for thermal fatigue failure of the Au/Ag interface.

Thermal fatigue and cracking behaviors of asphalt mixtures under different temperature variations

Thermal cracking is one of the most annoying distresses in asphalt pavements. The cracking of asphalt pavements caused by extremely low temperature and the damage of thermal fatigue caused by repeated temperature variations are particularly pronounced. The service condition of asphalt pavements has been affected significantly. Laboratory experiments with cyclic loads simulating the actions caused by repeated temperature variations on pavements have been conducted in many previous studies to investigate the thermal fatigue characteristics of asphalt mixtures. In those studies, an equivalent cyclic mechanical stress that can be applied by an actuator was mostly used to replace the cyclic thermal stress induced by a temperature variation. It could simplify the experimental process but could not consider the performances of asphalt mixtures varying as a function of temperature. In the present study, the thermal fatigue properties and cracking behaviors of asphalt mixtures were comprehensively investigated through a modified thermal stress restrained specimen test (TSRST) and the numerical analysis. Various temperature ranges (-20 to −10 °C, −10 to 0 °C), cyclic cooling rates (10 °C/h, 20 °C/h), low-temperature performance cooling rates (10 °C/h, 8 °C/h, 6 °C/h, 4 °C/h, 2 °C/h) and pre-crack dimensions were considered for the study to address the influences of those parameters on the analysis results. Based on the testing and simulation results, it was found that the effects of thermal fatigue on asphalt mixtures under different temperature variations and cooling rates were quantified, and the damage characteristics of the asphalt mixtures were also explored. The results showed that under the low-temperature performance state, the thermal stress of asphalt mixtures increases with a uniform cooling rate and it could be obtained that the faster the cooling rate, the larger the thermal stress generated. In the cyclic thermal stress test, due to the viscoelastic properties of asphalt mixtures, the thermal stress showed significant stress relaxation phenomena under the temperature variations. The magnitude of thermal stress decreased gradually within each cycle. It demonstrates that under the same temperature variation, the thermal stress decreases continuously with the increasing thermal cycles. Through the numerical simulation, it was clear that under different temperature ranges and cooling rates, the magnitude of thermal stress increased with the temperature range decreased, whereas the magnitude of thermal stress increased with an acceleration of the cooling rate. The lower temperature range induced a larger stress intensity factor (KI), which implies a faster cracking evolution. Analyzing the effects of different pre-crack dimensions on the number of temperature cycles, the height of pre-crack showed significant effects on the number of temperature cycles than width.

Kinetics of precipitation for graphite particle in high nickel ductile iron

In order to prevent premature failure of high nickel ductile iron used for engine exhaust manifold due to thermal fatigue, the precipitation morphology, nucleation and growth mechanism of graphite particles in high-nickel ductile iron were systematically studied by optical and SEM microscopy and the growth kinetic equation of graphite particles was derived. The results show that the precipitation density and average size of graphite particles within the austenite grain of high-nickel ductile iron are 44.1 particles/mm2 and 2.2 µm, respectively, and the precipitation density and average size of graphite particles on the austenite grain boundaries are increased to 76.6 particles/mm2 and 17 µm, respectively. The main nucleation mechanism of graphite particles in high nickel austenitic ductile iron is grain boundary nucleation. The maximum nucleation rate temperature of graphite particles nucleated on grain boundary is 650–850 °C, the fastest precipitation temperature is close to 680 °C, and the time from the beginning to the end of the growth of graphite particles nucleated by grain boundary is about 3400 s. The average size of graphite particles precipitated by grain boundary nucleation can grow to grade 7 (15–30 µm) under the high temperature of 715–805 °C for a long time (over 3400 s), which is beneficial to the thermal fatigue property of high nickel ductile iron. The local temperature at manifold should not be higher than 800 °C under long times.

Research Progress of Steels for Nuclear Reactor Pressure Vessels.

The nuclear reactor pressure vessel is an important component of a nuclear power plant. It has been used in harsh environments such as high temperature, high pressure, neutron irradiation, thermal aging, corrosion and fatigue for a long time, which puts forward higher standards for the performance requirements for nuclear pressure vessel steel. Based on the characteristics of large size and wall thickness of the nuclear pressure vessel, combined with its performance requirements, this work studies the problems of forging technology, mechanical properties, irradiation damage, corrosion failure, thermal aging behavior and fatigue properties, and summarizes the research progress of nuclear pressure vessel materials. The influencing factors of microstructures evolution and mechanism of mechanical properties change of nuclear pressure vessel steel are analyzed in this work. The mechanical properties before and after irradiation are compared, and the influence mechanisms of irradiation hardening and embrittlement are also summarized. Although the stainless steel will be surfacing on the inner wall of nuclear pressure vessel to prevent corrosion, long-term operation may cause aging or deterioration of stainless steel, resulting in corrosion caused by the contact between the primary circuit water environment and the nuclear pressure vessel steel. Therefore, the corrosion behavior of nuclear pressure vessels materials is also summarized in detail. Meanwhile, the evolution mechanism of the microstructure of nuclear pressure vessel materials under thermal aging conditions is analyzed, and the mechanisms affecting the mechanical properties are also described. In addition, the influence mechanisms of internal and external factors on the fatigue properties, fatigue crack initiation and fatigue crack propagation of nuclear pressure vessel steel are analyzed in detail from different perspectives. Finally, the development direction and further research contents of nuclear pressure vessel materials are prospected in order to improve the service life and ensure safe service in harsh environment.

Dynamic mechanical properties of FGH4097 powder alloy and the applications of its constitutive model

As a typical multiphase alloy, FGH4097 has good lasting strength (thermal stability and thermal fatigue properties), excellent wear resistance and heat resistance. It has been widely used in aerospace and other hot-end parts manufacturing fields. Most of the existing researches on the mechanical properties of FGH4097 alloy are carried out at low strain rate. There is no effective research on high temperature dynamic mechanical properties of FGH4097. Through the impact compression test of FGH4097 under different strain rates and different temperature conditions by the split Hopkinson compression bar equipment, the corresponding true stress-true strain curve was obtained, the strain rate sensitivity and temperature sensitivity of the material were analyzed. The specific heat capacity of FGH4097 alloy at different temperatures was measured by a laser thermal conductivity meter, and the adiabatic temperature rise of the alloy at different temperatures and strain rates was studied. The isothermal true stress-strain curve of the alloy was obtained by calculating the thermal softening coefficient. Two constitutive equations, Johnson-Cook and Power-Law, were introduced to fit and characterize the dynamic mechanical properties of FGH4097 alloy at different strain rates and temperatures, and the corresponding material constitutive models were obtained. Comparing the fitting accuracy of the two models, it is found that the fitting accuracy of the Power-Law model is higher, with an average error of less than 8%. The cutting simulation of FGH4097 alloy was carried out by AdvantEdge software, and the effects of strain and strain rate on the machinability of FGH4097 alloy were investigated.

Effect of Cr–N precipitations on thermal fatigue behaviour of GX-8 steel nitrided layer

Two types of nitrided layers with different nitride precipitates were prepared by salt bath nitriding on the surface of GX-8 steel. The microstructure of the nitrided layers was investigated by SEM, XRD, grazing-incidence XRD and TEM. A cyclic thermal fatigue test system was used to evaluate the influence of nitrides on the thermal fatigue properties of the two nitrided layers. Under the operation of alternating thermal cycles from ambient temperature to 600 °C on the surface, the nitrided surface with a compound layer composed of ε-Fe2-3N phase and strip-shaped CrN had more cracks and spalling than that of the nitrided layer with nanoscale nitrides. Further analysis revealed that the tessellated stress caused by different thermal expansion coefficients of CrN and α-Fe in the interlayer was responsible for the interlaminar deformation, cracking and spalling of the surface.

Effect of Cr, Mo, and V Elements on the Microstructure and Thermal Fatigue Properties of the Chromium Hot-Work Steels Processed by Selective Laser Melting

Thermal fatigue is the main failure mode for chromium hot-work steels. In this study, pre-alloyed chromium hot-work steel powders with three different Cr, Mo, and V addition levels (low content (LH), medium content (MH), and high content (HH)) were used for selective laser melting (SLM). The microstructure and thermal fatigue properties of these SLM-processed materials were investigated. After thermal fatigue tests, LH possessed the lowest hardness (approximately 573 HV5) and longest crack length, MH possessed the highest hardness (approximately 688 HV5) and HH (with the hardness of approximately 675 HV5) possessed the shortest crack length. It can be concluded that the increase of V content in MH is the main reason for the refined grains which result in an enhanced hardness and thermal fatigue resistance compared to LH. The further increase of the Cr and Mo content in HH leads to the grain coarsening and hardness decreasing, which is supposed to degrade the thermal fatigue resistant properties according to the conventional theory. However, HH exhibited an enhanced thermal fatigue resistance compared to MH. That is because the higher stored energy in MH deteriorated its thermal fatigue resistance compared to HH.