Long-term Thermal Exposure Research Articles

Elevated-temperature performances of Al-Si-Cu casting alloys for cylinder head applications

In this study, high-temperature properties of two newly developed Al-Si-Cu alloys (2Cu and 3.5Cu alloys) were investigated and compared to the commercial-grade A356 + 0.5Cu alloy (R alloy). 3.5Cu alloy exhibited the highest strength, outperforming R alloy by over 50 MPa at room temperature and by more than 20 MPa at elevated temperatures in ultimate tensile strength. However, R alloy demonstrated three to four times higher elongation than 3.5Cu alloy at room temperature, though this difference diminished at high temperatures. The minimum creep rate of 3.5Cu alloy was 2.4 times lower than that of 2Cu alloy and 14.5 times lower than that of R alloy, showing the superior creep resistance. Under low cycle fatigue loadings, the fatigue lifetimes of R and 2Cu alloys were similar, and slightly longer than that of 3.5Cu alloy. Conversely, in the high cycle fatigue regime, 3.5Cu alloy exhibited the highest fatigue resistance, followed by 2Cu and R alloys. The superior high-temperature performances of 3.5Cu alloy were attributed to the enhanced thermal stability of θ' precipitates compared to β' precipitates in R alloy, as confirmed during long-term thermal exposures at 250 and 300 °C. These findings suggest that 3.5Cu alloy is a promising candidate to replace the traditional A356 + 0.5Cu alloy for cylinder head applications.

Influence of Si on the Elevated-Temperature Mechanical and Creep Properties of Al–Cu 224 Cast Alloys during Thermal Exposure

The influence of Si content (0.1–0.8 wt.%) on the development of precipitation microstructures and the resultant mechanical and creep properties during thermal exposure, up to 1000 h at 300 °C, in Al–Cu 224 cast alloys, was systematically investigated. The room and elevated temperature yield strength (YS) increased with increasing Si content under the T7 condition, which was attributed to the fact that the Si promoted the precipitation of fine θ′. However, Si increased the coarsening of θ′ during thermal exposure at 300 °C, and the alloys with low Si exhibited a higher YS and creep resistance at elevated temperatures than high Si alloys. The mechanical strength and creep resistance were mainly controlled by the precipitation strengthening of the predominant θ′ phase. Because of the high mechanical strength and creep resistance of the 0.1Si alloy during long-term thermal exposure, the Si level in Al–Cu alloys should be maintained at a low level of 0.1 wt.% for high-temperature applications. The strengthening mechanisms were quantitatively analyzed, based on the characteristics of the precipitate. The predicted YS values under different exposure conditions agreed well with the experimentally measured values.

Effects of Thermal Exposure Temperature on Room-Temperature Tensile Properties of Ti65 Alloy.

As a critical material for high-temperature components of aero-engines, the mechanical properties of Ti65 alloy, subjected to high-temperature and long-term thermal exposure, directly affect its service safety. The room-temperature tensile properties of the Ti65 alloy after thermal exposure to temperatures ranging from 450 °C to 650 °C for 100 h were investigated. The results indicate that as the thermal exposure temperature increases, the strength of Ti65 alloy initially increases and then decreases, while ductility exhibits a decreasing trend. The strength of the thermally exposed alloy positively correlates with the size and content of the α2 phase. The ductility of the thermally exposed alloy is comprehensively influenced by the surface oxidation behavior, α2 phase, and silicides. After the prolonged thermal exposure, stress concentration at the crack tips within the oxide layer was enhanced with the increased thickness of the surface TiO2 oxide layer, leading to premature fracture due to reduced alloy ductility. Furthermore, the α2 phase in the matrix promotes the planar slip of dislocations, while silicides at the α/β phase boundaries hinder dislocation motion, causing dislocation pile-ups. Both behaviors facilitate crack nucleation and deteriorate alloy ductility.

Effect of Phase Composition Variation of Oxy–Nitride Composite Ceramics on Heat Resistance and Preservation of Strength Parameters

The aim of this study is to determine the effect of changes in the phase composition of Al2O3–Si3N4 ceramics that were obtained using the method of mechanochemical solid-phase grinding on their resistance to the process of long-term thermal exposure, accompanied by the processes of oxidation and softening. The relevance of this research consists of determining the influence of the phase composition of ceramics on the change in their strength and thermophysical parameters, on the basis of which, we can draw a conclusion about the optimal composition of composite ceramics that have great prospects in the field of fire-resistant, heat-resistant, or radiation-resistant structural materials. During this study, the dynamics of the changes in the phase transformations of the xAl2O3–(1−x)Si3N4 ceramics, with variations in the ratio of the components, initiated by the thermal annealing of the samples, was established. According to the assessment of the phase transformations with variations in the ratio of the components, it was found that thermal annealing in an air environment at an Al2O3 concentration in the order of 0.3–0.5 M leads to the formation of an orthorhombic Al2(SiO4)O phase and an elevation in its contribution at concentrations above 0.5 M, which causes a rise in the thermophysical parameters and resistance to high-temperature degradation. During the heat resistance tests, it was found that the formation of the composite ceramics with the Si3N4(SiO2)/Al2(SiO4)O/Al2O3 phase composition results in an increase in the stability of their strength properties when exposed to thermally induced oxidation, which has a negative impact on their resistance to softening and a decrease in hardness. Moreover, the presence of the Al2(SiO4)O phase in the composition of the ceramics causes a slowdown in the processes of thermal oxidation of the Si3N4 phase under prolonged temperature exposure, alongside an increase in the degradation resistance of strength properties by more than 4–7 times, in comparison with the softening data established for single-component ceramics.

Microstructural Evolution and Subsequent Mechanical Properties of Ti65 Titanium Alloy during Long-Term Thermal Exposure

Microstructural Evolution and Subsequent Mechanical Properties of Ti65 Titanium Alloy during Long-Term Thermal Exposure

Effect of μ precipitation and γ′ evolution on intra-/intergranular strength of Ni-Co-Cr-based superalloys after 800 ℃ thermal exposure

The initiation of microscopic defects and the microstructural stability are crucial factors in determining the tensile strength and failure mechanism of Ni-Co-Cr-based superalloys. This study involved the long-term thermal exposure of Ni-Co-Cr-based superalloys at 800 ℃ and their elevated-temperature tensile testing at 750 ℃ to investigate the microstructural and properties evolution. A 100 h-exposure led to the formation of a significant number of μ precipitates rich in refractory elements at the grain boundaries, particularly on the large-sized γ′ precipitate surfaces. The intragranular γ′ precipitates considerably coarsened with an increasing thermal exposure duration while its volume fraction remained relatively constant. Cracks tended to nucleate preferentially at the μ phase interface during high-temperature tensile testing, leading to the breakage of the γ/γ′ precipitates and formation of pores owing to crack propagation. The dislocation motion as a deformation response of the intragranular γ/γ′ precipitates to tensile testing was dominated by a shearing mechanism, with a portion of the intragranular γ′ precipitates deforming through dislocation shearing. The primary failure mechanism during high-temperature tensile testing changed from intergranular to intragranular with an increasing exposure time. Investigating the relationship between the phase evolution and failure mechanism will enhance our understanding of the fracture behavior of Ni-Co-Cr-based superalloy hot-end structural parts.

Failure mechanisms for Gd2O3–Yb2O3 co-doped YSZ thermal barrier coatings under high-temperature gradient

In this study, Gd2O3–Yb2O3 co-doped YSZ thermal barrier coatings with a top coat thickness of 400 μm were prepared on a nickel-based superalloy by atmospheric plasma spraying. The samples underwent multiple short-term and single long-term thermal exposures through burner rig tests under high-temperature gradients. The short-term thermal exposure duration of the coating was 25 s and the long-term thermal exposure duration was 1200 s. The microstructures and phase compositions of the samples were characterized, and their failure mechanism was discussed. The results demonstrate that during the burner rig tests, the coating surface temperature reached 2600K, resulting in coating sintering and sintered zone formation comprising coarse equiaxed grains. The short-term thermal exposure life of the coating is 3 cycles, and the long-term life is more than 1200s. After the single 1200s thermal exposure, the coating exhibited a stable cubic phase. However, under multiple 25s thermal exposures, the depth of the sintered zone increased with increasing number of cycles, leading to the formation of various vertical and transverse cracks within the coating. Coating failure was due to a combination of sintering and thermal-mismatch-induced stress.The early-stage coating delamination was attributed to sintering-induced transverse cracks, while the overall spallation was primarily ascribed to thermal-mismatch-induced transverse cracks.

Effects of phosphorus and boron on the γ″ precipitate evolution and creep properties of IN718 superalloy during long-term thermal exposure at 680 ℃

A study was conducted to investigate the effect of the combined addition of P and B on the γ″ precipitate and creep properties of IN718 superalloy under long-term thermal exposure at 680 ℃. Atomic probe tomography (APT) analysis and X-ray diffraction (XRD) results indicated that P could segregate in the γ″ precipitates in a substitutional way and then improve the stability of the γ″ precipitates when subjected to prolonged thermal exposure. No segregation of B was found in the γ″ precipitates. The addition of P and B significantly improves the creep properties of the IN718 superalloy during long-term thermal exposure at 680 ℃. By increasing the exposure time, the creep life of the high P and B alloy at 650 ℃/725 MPa initially increased, peaking at 500 h, and then decreased as the exposure time increased. However, the low P and B alloy shows a consistent decrease in creep life with increasing thermal exposure time. During a relatively short thermal exposure, the microstructural analysis indicated that the substantial enhancement in creep life of the high P and B alloy primarily stems from cross twins and Lomer-Cottrell (LC) locks. As the thermal exposure time increases, the more stable γ″ precipitates in the high P and B alloy, which directly improves the creep properties. The dominant deformation mechanism in the two alloys shifts from predominantly twin to a combination of twin, stacking fault (SF) and antiphase boundary-like (APB-like) shear γ″ precipitate with prolonged thermal exposure.

Understanding the fracture mechanisms of Ni–Co–Cr-type superalloys: Role of precipitate evolution and strength degradation

Microstructure stability directly affects the performance degradation of hot-end structural parts such as turbine discs. In this research, long-term (10–10000 h) thermal exposure experiments were conducted on a Ni–Co–Cr type superalloy at 800 °C. The mechanical properties were obtained through high-temperature (750 °C) tensile tests. Subsequently, the microstructure evolution process, including intragranular γ′ and μ phases, and the initiation and propagation of defects were systematically and thoroughly studied. The results showed that intragranular γ′ precipitates coarsened under thermal exposure. After 100 h of thermal exposure, μ phases were observed near the intergranular γ′ precipitates and grain boundaries. The size and volume fraction of the μ phase initially increased, and then remained relatively stable. Numerous cracks formed on the plane of the μ phases and intergranular γ′ precipitates. With an increase in tensile stress, these cracks interconnected and propagated along the intergranular γ′ precipitates, leading to the formation of pores. Moreover, because the size of the intragranular γ′ precipitates exceeded 80 nm, the critical resolved shear stress (CRSS) was primarily activated by the Orowan bypassing mechanism. Notably, the CRSS of dislocation motion, such as stacking fault, strong-coupled shearing, and Orowan bypassing, decreased with increasing intragranular γ′ precipitate size. Therefore, the intragranular strength also weakened and the intragranular γ′ precipitates coarsened under continuous thermal conditions. This research on precipitate evolution and failure mechanisms will contribute to a better understanding of failure mechanisms for Ni–Co–Cr-based superalloys.

Achieving superior elevated temperature properties in additive manufactured nickel-based superalloys through unique alloy design

Additive manufacturing (AM) offers a new solution for the integrated fabrication of complex components, supplementing the shortcomings of conventional subtractive manufacturing. However, the forming defects owing to alloy unsuitability and the lack of long-term service stability of the components seriously limit its widespread engineering applications. Here we developed a nickel-based superalloy, Haynes 230AM, suitable for AM by using Zirconium (Zr) alloying strategy in Haynes 230 alloy, which is crack-free and has outstanding elevated temperature properties. Compared with commercial Haynes 230 alloy fabricated by rolling and AM, the printed Haynes 230AM in our work achieves about 700 % improvement in creep lifetime, breaking the status quo that the creep properties of AM fabricated alloys are generally inferior to the corresponding conventional manufactured alloys. Our results reveal that the introduction of Zr element optimized the microstructure of the alloy. The superior creep resistance of Haynes 230AM stems from the uniform distribution of fine ZrC carbide, the precipitation of Ni7Zr2 phase along close-packed planes and the formation of unique matrix distortion stripes, which impede dislocation motion and delay the formation of creep defects. Moreover, the Zr element can also improve internal oxide scales, reduce oxidation weight gain by 20 % and does not deteriorate the mechanical properties after long-term thermal exposure. These results can provide guidance for the design of high-performance AM-specific superalloys.

Mechanical degradation behavior and γ′ coarsening mechanism of a Ni-based superalloy during long-term high-temperature thermal exposure

Aero engine design necessitates crucial components, such as turbine discs, to be highly stable in high-temperature environments. Therefore, the accurately determining of the mechanical properties and microstructure evolution of these components under long-term high-temperature exposure is ofs significant engineering and scientific value. Herein, we systematically analyzed the microstructure and performance evolution of a Ni-based superalloy during long-term high-temperature exposure, explored the relationship between service conditions and yield strength, and introduced novel strength decay factors, namely temperature (|α|) and time (|β|) decay factors. |α| was strongly positively correlated with the exposure temperature, whereas |β| exhibited a more complex behavior and was more affected by the microstructure before thermal exposure, especially at low temperatures (650–700 °C). Microstructural analysis revealed minimal changes in average grain size and Σ3 twin boundaries following long-term thermal exposure. However, γ′ particles coarsened after thermal exposure, particularly at higher temperatures and longer exposure times. The coarsening process under different conditions was examined using Lifshitz–Slyozov–Wagner and trans-interface diffusion-controlled models. The coarsening of γ′ particles led to mechanical degradation, as the critical failure stress decreased with increasing γ′-particle size.

Microstructural Evolution and Tensile Properties of Al-Si Piston Alloys during Long-Term Thermal Exposure

The present study investigated microstructural evolution and changes in tensile properties of an Al-Si piston alloy subjected to thermal exposures at 250 and 350 °C for 150, 300, and 500 h. Microstructural and nanoscale precipitates were characterized using a combination of high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images and scanning electron microscopy (SEM). The tensile testing was performed. The results demonstrated that the thermal exposure induced granulation of the δ-Al3CuNi particles, alongside precipitation of the θ-Al2Cu phase particles and AlCu clusters within the matrix. Specifically, an increase in the size and number density of the θ-Al2Cu phase particles was observed with exposure time at 250 °C. Conversely, at 350 °C, the θ-Al2Cu particles exhibited a gradual increase in size with prolonged thermal exposure, coupled with a decrease in their number density. AlCu clusters precipitated solely at a thermal exposure temperature of 350 °C, with precipitation intensifying over time. Moreover, a decrease in the alloy’s tensile strength and an increase in elongation were noted after thermal exposure. Finally, the present study discussed the precipitation mechanisms of θ-Al2Cu particles and AlCu clusters within the grains, suggesting that the AlCu clusters exerted a more effective strengthening effect compared to the θ-Al2Cu particles.

Improving long-term thermal stability in twin-roll cast Al-Mg-Si-Cu alloys by optimizing Mg/Si ratios

Achieving high thermal stability in the 6xxx series alloys remains a challenging task, which limits their engineering application. Herein, Al-Mg-Si-Cu alloys with various Mg/Si ratios (0.5, 1, 2, and 4) were fabricated by twin-roll casting (TRC), and the microstructure evolution and mechanical properties during long-term thermal exposure of 150 °C/1000 h were studied. The results disclosed that alloys with a high Mg/Si ratio exhibited better thermal stability. The alloys with the Mg/Si ratio of 2 (Mg/Si∼2) achieved a stable high yield strength of ∼330 MPa and meanwhile maintained a satisfactory fracture elongation (> 10 %) throughout the thermal exposure process. This excellent thermal stability can be attributed to the microstructure consisting of high-density L phases and fine α-AlFeSi phases, which was related to the optimized Mg/Si ratio. Specifically, L phases were dominated in peak-aged Mg/Si∼2 alloys, while the counterparts in alloys with the Mg/Si ratio of 1 (Mg/Si∼1) were β'' and Q' phases. During the thermal exposure process, the L phases remained stable without coarsening, which was mainly due to the high coherence and low interfacial energy of the L-matrix interface. Meanwhile, the main Fe-containing phases in Mg/Si∼2 and Mg/Si∼1 alloys were fine near-spheroidal α-AlFeSi and large-size needle-like β-AlFeSi, respectively, which lead to a better ductility of Mg/Si∼2 alloys. This work may provide a strategy for the preparation of 6xxx series alloys with high thermal stability.

Tensile creep behavior of the Nb45Ta25Ti15Hf15 refractory high entropy alloy

The tensile creep behavior of a vacuum arc-melted Nb45Ta25Ti15Hf15 refractory high entropy alloy was investigated over a constant true stress range of 50–300 MPa at a temperature of 1173 K. Creep tests were carried out in both high vacuum (5 × 10−6 torr) and ultrahigh purity Ar gas to examine the environmental effect. The samples tested in vacuum exhibited power law behavior with a stress exponent of 4.1 and exceptional tensile creep ductility, whereas those tested in Ar suffered significant embrittlement due to HfO2 formation at grain boundaries, which was exacerbated at low applied stresses where extended exposure to residual O2 gas resulted in more extensive brittle intergranular fracture. Phase decomposition occurred after long-term thermal exposure, where a second Hf-rich body-centered cubic phase formed predominantly at grain boundaries but did not cause embrittlement. Compared to the equiatomic TaNbHfZrTi (Senkov alloy) and face-centered cubic multiple-principal element alloys, Nb45Ta25Ti15Hf15 has superior creep resistance, especially at high applied stresses, while maintaining excellent creep ductility. Transmission electron microscopy revealed that creep deformation in Nb45Ta25Ti15Hf15 at 1173 K is controlled by cross-kink collisions from screw dislocations that results in dipole drag at lower strain rates and jog drag at higher strain rates.

Impact of long-term thermal exposure on the microstructure and creep resistance of (TiB+TiC+Y2O3)/α-Ti composite

In this study, the influences of thermal exposure on the microstructure and creep resistance of matrix alloy and (TiB+TiC+Y2O3)/α-Ti composites were systematically studied. The results indicate that long-term thermal exposure leads to β-Ti dissolution, as well as the precipitation of a large number of S1 type silicides and α2 particles. The high temperature and internal stress by thermal exposure promote β-Ti→α-Ti phase transition. In order to reduce the total energy, nanoscale {101̅1} transformation twins were formed at the α/β interfaces. The introduction of precipitates and nano twins leads to a significant improvement in the creep resistance after thermal exposure. The creep life can be increased by up to 108 %, while the steady-state creep rate can be reduced by an order of magnitude. After creep, there was no significant increase in the size of precipitated silicides and α2 particles. The rod-shaped S1 type silicide has a better pinning strengthening effect on dislocations than spherical S2 type silicide. Nano twins improve the stability of the α/β interfaces during creep. Some twins were coarsened after creep by merging mechanism. Twins and reinforcements provide nucleation sites for sub-grains during the creep process.

The effect of Hafnium on the microstructure and tensile property in a Ni-based superalloy

The effects of Hafnium on the microstructure and tensile property of a Ni-based superalloy after solution heat treatment and long-term thermal exposure were investigated with field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD). The results revealed reveal that Hf intensified intensifies the element segregation and promoted promotes the precipitation of MC carbide and honeycomb-like Ni5Hf phase in the as-cast alloy. The solid solution strengthening and second phase (MC) strengthening effects are both enhanced in the alloy doping 0.5 wt% Hf after solution heat treatment. Therefore, the tensile yield strength at 700 °C of the alloy with 0.5 wt% Hf is higher than that in the Hf-free alloy. Otherwise, a large amount of the low melting point Ni5Hf phases appear in the alloy with 0.8 wt% Hf. Ni5Hf phase is prone to become the crack initiation, which decreases diminishes the yield strength in the alloy with 0.8 wt% Hf. The addition of 0.5 wt% Hf can inhibit the formation of needle-like δ phase at grain boundary due to the decrease of grain boundary energy and diffusion rate at grain boundary. Therefore, the 700 °C tensile strength and ductility increase simultaneously in the alloy with 0.5 wt% Hf after thermal exposure at 700 °C.

Precipitation and tensile behaviors of Allvac 718Plus superalloy during long-term thermal exposure

Allvac 718Plus alloy is a promising Ni-based superalloy with excellent thermal stability and mechanical properties up to 704 °C. The γ′ coarsening, σ precipitation and the resulting degraded tensile properties at room and elevated (704 °C) temperatures during long-term thermal exposure at 704 and 760 °C are systematically investigated in this work. The results showed that a higher exposure temperature and a longer exposure time significantly accelerate the γ′ coarsening and σ precipitation. The σ particles were detrimental to the alloy by acting as the preferential nucleation sites for cracks, and the reduction in tensile strengths was mainly caused by the increasing size of γ′ precipitates during thermal exposure. Furthermore, there were significant differences between the deformation mechanisms of room-temperature and elevated-temperature (760 °C) tensile tests. Concerning the deformation mechanism of γ-matrix, planar slipping dominates during tensile testing at room temperature, while the formation of stacking faults and microtwinning are primary during tensile testing at elevated temperature (760 °C). The dominant precipitation strengthening mechanism depended on the γ′ characteristics of different thermal exposure conditions and the tensile temperature. The 704 °C/100 h exposure sample shows a dislocation shearing mechanism when tested at room or elevated (760 °C) temperature. Notably, the 760 °C/1000 h exposure sample exhibits a mixed precipitation strengthening mechanism of Orowan bypassing and superlattice stacking faults shearing when tensile tested at room temperature while showing a dislocation and superlattice stacking faults shearing mechanism when tensile tested at elevated (760 °C) temperature.

Effect of thermal exposure on the microstructure and mechanical properties of Ti60 alloy

The effect of thermal exposure on the microstructure and mechanical properties of Ti60 alloy was investigated in the present study. Meanwhile, the fatigue fracture microscopic appearance characteristics at elevated temperature were analyzed compared, providing the basis to further improve the performance of the series of high temperature titanium alloy. The results show that the yield strength and tensile strength were basically stable under long-term thermal exposure below 600°C, while the elongation decreased with the increase of exposure temperature. Thermal exposure below 800°C did not change the microstructure type of Ti60 alloy, but at higher temperature local β coursing occurred at the grain boundary. When the alloy was exposed above 600°C, Si was obviously concentrated in the grain boundary region, and the maximum concentration was up to 2.5%. With the increase of thermal exposure temperature, the characteristics of high-temperature fatigue fracture of Ti60 alloy change from trans-granular toughness to intergranular brittleness.

A New Al2 O3 -Protected EB-PVD TBC with Superior CMAS Resistance.

Calcium-magnesium-aluminium-silicate (CMAS) attack is a longstanding challenge for yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) particularly at higher engine operating temperature. Here, a novel microstructural design is reported for YSZ TBCs to mitigate CMAS attack. The design is based on a drip coating method that creates a thin layer of nanoporous Al2 O3 around YSZ columnar grains produced by electron beam physical vapor deposition (EB-PVD). The nanoporous Al2 O3 enables fast crystallization of CMAS melt close to the TBC surface, in the inter-columnar gaps, and on the column walls, thereby suppressing CMAS infiltration and preventing further degradation of the TBCs due to CMAS attack. Indentation and three-point beam bending tests indicate that the highly porous Al2 O3 only slightly stiffens the TBC but offers superior resistance against sintering in long-term thermal exposure by reducing the intercolumnar contact. This work offers a new pathway for designing novel TBC architecture with excellent CMAS resistance, strain tolerance, and sintering resistance, which also points out new insight for assembly nanoporous ceramic in traditional ceramic structure for integrated functions.

Effects of short and long-term thermal exposure on microbial compositions in soils contaminated with mixed benzene and benzo[a]pyrene: A short communication

Polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX) are the most persistent and toxic organic contaminants often found co-contaminated in anthropogenic and petrochemical industrial sites. Therefore, an experiment was performed for the safe biodegradation of benzene and benzo[a]pyrene (BaP) through thermally-enhanced biodegradation, and to explore the influence of elevated thermal treatments on microbial diversity and composition. The results revealed that elevated thermal treatments (15 to 45 °C) significantly enhanced the diversity of both bacteria and fungi. The composition analysis revealed that short-term and long-term elevated temperature conditions can directly enhance the specificity of microorganisms that play a crucial role in the biodegradation of benzene and BaP co-contaminated soil. Moreover, the indirect role of elevated temperature conditions on microbial compositions was through the fluctuations of soil properties, especially soil pH, moisture, TOC, potassium, phosphorous, total Fe, Fe(II), and Fe(III). In addition, the correlation analyses revealed that thermal exposure enhances the synergistic association (fungal-fungal, fungal-bacterial, bacterial-bacterial) of microbes to degrade the toxic contaminants and to cope with harsh environmental conditions. These results concluded that the biodegradation of benzene and BaP co-contamination was efficiently enhanced under the thermally-enhanced biodegradation approach and the elevation of temperature can affect the microbial compositions directly via microbial specificity or indirectly by influencing the soil properties.