Nanoindentation Results Research Articles

Enhanced ductility and thermal stability of TZM alloys via nanoscale second phase

In this study, molybdenum alloy with the nanoscale second phase dispersion distribution (NM-TZM) was prepared by powder metallurgy. Despite maintaining a high yield strength of 893 MPa, the elongation of the as-forged MN-TZM alloy has been increased to 25.3 %. In addition, the recrystallization start temperature of NM-TZM alloy was increased by 100 °C, reaching 1400 °C. The nanoindentation results indicate that the NM-TZM alloy still exhibits a high hardness of 4.40 GPa following annealing at 1400 °C. The addition of nanoscale second phase can improve the ductility and high temperature stability of the alloy by coupling with dislocations and grain boundaries. A new model for the synergistic effect of grain boundaries and intragrains to improve ductility is proposed, which provides insight into the reason behind the high ductility of NM-TZM.

Optimization of the Microstructure and Mechanical Properties of a TC4 Alloy Joint Brazed with a Zr-Based Filler Containing a Co Element.

Herein, we fabricated a low-melting-point Zr-16Ti-6Cu-8Ni-6Co eutectic filler based on a Zr-Ti-Cu-Ni filler to achieve effective joining of a Ti6Al4V (TC4) titanium alloy. The temperature at which the brittle intermetallic compound (IMC) layer in the seam completely disappeared was reduced from 920 °C to 900 °C, which broadened the temperature range of the Zr-based filler, brazing the TC4 without a brittle IMC layer. The shear strength of the Zr-16Ti-6Cu-8Ni-6Co brazed joint increased by 113% more than that of the Zr-16Ti-9Cu-11Ni brazed joint at 900 °C. The proportion of β-Ti in the seam of the Zr-16Ti-6Cu-8Ni-6Co brazed joint increased by 21.31% compared with that of the Zr-16Ti-9Cu-11Ni brazed joint. The nano-indentation results show that the elastic modulus of the β-Ti (143 GPa) in the interface is lower than that of the α-Ti (169 GPa) and (Ti,Zr)2(Ni,Cu,Co) (203 GPa). As a result, the β-Ti is subjected to a greater strain under the same stress state compared with the α-Ti and (Ti,Zr)2(Ni,Cu,Co), and the Zr-16Ti-6Cu-8Ni-6Co brazed joint can maintain a higher strength than the Zr-16Ti-9Cu-11Ni brazed joint under a middle-low erosion area of the TC4 base metal. This provides valuable insights into the use of high-strength, fatigue-resistant TC4 brazed joints in engineering applications.

Effect of heat treatment on wear resistance of cold-sprayed Ti-diamond composite coating

In order to enhance the wear resistance of cold-sprayed Ti coatings, Ti-diamond (Ti-MD) composite coatings were fabricated, followed by heat treatment at different temperatures. The effects of heat treatment temperature on the wear resistance of the composite coatings were assessed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), microhardness testing, and wear resistance experiments. The results show that the composite coating undergo no phase transformation after heat treatment, and exhibits higher microhardness and improved wear resistance. The porosity results showed that the porosity of the coating decreased as the heat treatment temperature increases. TEM results showed that stable TiC (about 10 nm) was formed at the interface between the titanium and diamond particles after heat treatment at 800 °C, and nanoindentation results showed that the heat-treated coating had higher deformation resistance. Specifically, when the heat-treated temperature rose to 800 °C, the composite coating exhibits an 80 % reduction in wear rate, primarily attributable to the decreased porosity of the coating and the enhanced adhesion between Ti and diamond particles. The wear mechanisms of the heat-treated coatings are predominantly reduced oxidative and abrasive wear.

Carbonation of one-part alkali-activated materials incorporated by MgO: Phase characteristics and micromechanical properties

The role of magnesium oxide (MgO) in the carbonation of cementitious materials, particularly alkali-activated materials (AAM), which is a promising low-carbon alternative to ordinary Portland cement (OPC), has garnered significant attention. However, there remains a lack of clear understanding regarding its underlying mechanisms and interrelation with calcium oxide (CaO) content. This study aims to understand the influence of MgO on carbonation mechanisms, carbonation products, and (C, N)–A–S–H gel micromechanical properties in AAM. Four different binder formulations were examined by varying contents of slag, class F fly ash, and light-burned MgO. A powder-type sodium metasilicate was used as an alkaline activator. CO2 curing was conducted in a CO2 incubator with 1 % concentration and under atmospheric pressure for up to 56 days using pulverized paste binders. The carbonation mechanism, polymorphs of carbonation products, and the micromechanical properties of the (C, N)–A–S–H gel matrix were characterized by conducting laboratory tests including pH measurement, XRD, TGA, DSC, nitrogen adsorption, and nanoindentation at various carbonation stages. A noticeable pattern of pH initially dropping and then rising was observed. Integrated XRD-TGA demonstrated the evolution, polymorphism, and amount of calcium carbonate phases. Higher MgO content in AAM binders favored the formation of aragonite and hydrotalcite. Extensive nanoindentation results and their statistical analysis revealed binder-specific trends in the pozzolanic matrix stiffness before and after carbonation. The findings of this study can be used in developing AAM binders as building materials and to provide a deeper understating of the carbonation reactions in AAM binders.

Investigation of microstructural and mechanical properties of sputter-deposited Ni3Al films at different substrate temperatures

Ni3Al films were deposited on silicon (100) substrate at different substrate temperatures by DC magnetron sputtering. The evolution of phase, microstructure, surface topography and mechanical properties have been investigated as a function of substrate temperature via XRD, FE-SEM, AFM and nanoindentation respectively. Results revealed that the deposited film possessed the preferred orientation of (111) whereas the crystallite size increased and grain size decreased with increase in the substrate temperature. The results of nanoindentation showed that the hardness of the film increased up to 400 °C after which it abruptly decreased. Maximum hardness of ∼13 GPa was achieved when the film was deposited at the substrate temperature of 400 °C. The surface roughness of the film increases simultaneously with the increase in substrate temperature whereas the static contact angle and mechanical properties declined significantly for the film deposited at the substrate temperature of 600 °C. This study reflects the impact of substrate temperature on the evolution of phase, microstructure and mechanical properties of Ni3Al coatings deposited at different substrate temperatures.

Nanomechanical and microstructural properties of experimental bilayered zirconia ceramics after hydrothermal aging

Two experimental ceramic systems, 3Y-TZP/5Y-PSZ (3Y/5Y) and 4Y-PSZ/5Y-PSZ (4Y/5Y), underwent analysis before (3Y/5Yi or 4Y/5Yi) and after hydrothermal aging (3Y/5Ya or 4Y/5Ya) to simulate low-temperature degradation (LTD). The samples were sintered and characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy, alongside nanoindentation tests to measure elastic modulus (Em) and hardness (H). Assessments were conducted on the external surfaces and at individual layers on cross-sectioned samples at predetermined regions of interest (ROIs). Degraded superficial regions were observed in the cross-sectional SEM images of the 3Y and 4Y zirconia layers after aging. XRD indicated a tetragonal→monoclinic phase transformation in the aged groups for both 3Y (66 % m-ZrO2) and 4Y (29 % m-ZrO2). Raman spectroscopy revealed monoclinic phase amounts of 86 % for 3Y and 62 % for 4Y in the degradation regions observed in the SEM micrographs. Monoclinic phase peaks were virtually no longer detected in either material beyond a depth of 15 μm. Hydrothermal aging significantly diminished the H and Em values for the 3Y and 4Y zirconia surfaces. For the analysis of different zirconia surfaces within the same subgroup, all pairwise comparisons showed statistically significant differences, except for the values of H of 3Y/5Yi and Em for 4Y/5Yi. Regarding the nanoindentation results of cross-sectioned samples, the aging protocol did not affect the H and Em values of the equivalent ROIs (layers), regardless of the bilayered system. However, significant differences in H values were observed among the ROIs (layers) within the same bilayered system. Despite surface changes, nanomechanical properties remained preserved below the surface and at the interfaces of bilayered materials after aging. Nanoscale H values varied among some layers and interfaces, whereas the Em values exhibited differences across certain surfaces.

Achieving in-situ Fe-based spherical particles for magnetic abrasive finishing process of Zirconium tube via gas nitriding method

The magnetic abrasive powders have great influence on the magnetic abrasive finishing accuracy and efficiency. A new kind of Fe-based spherical magnetic abrasive particles with Fe2N precipitates and Fe4N matrix was successfully synthesized by gas nitriding. The results show that the prepared Fe-based magnetic abrasive particles can reduce the roughness of the Zirconium tube from 0.325 to 0.154 μm by four MAF passes. The high hardness and wear resistance of the Fe-based magnetic abrasive particles are assessed based on the Vickers hardness and nanoindentation results. This study can provide theoretical and experimental support for fabricating high-performance magnetic abrasive particles.

Nanomechanical inhomogeneities in CVA-deposited titanium nitride thin films: Nanoindentation and finite element method investigations

Refractory metals that can withstand at high temperatures and harsh conditions are of utmost importance for solar-thermal and energy storage applications. Thin films of TiN have been deposited using cathodic vacuum arc deposition at relatively low temperatures ∼300 °C using the substrate bias ∼ −60 V. The nanomechanical properties of these films were investigated using nanoindentation and the spatial fluctuations were observed. The nanoindentation results were simulated using finite element method through Johnson-Cook model. A parametric study was conducted, and 16 different models were simulated to predict the hardening modulus, hardening exponent, and yield stress of the deposited film. The predicted values of elastic modulus, yield stress, hardening modulus and hardening exponent as 246 GPa, 2500 MPa, 25000 MPa and 0.1 respectively are found to satisfactorily explain the experimental load-indentation curves. We have found the local nitridation plays an important role on nanomechanical properties of TiN thin films and confirms that the nitrogen deficient regions are ductile with low yield stress and hardening modulus. This study further opens the opportunities of modelling the nanoscale system using FEM analysis.

Influence mechanism of original components on mechanical properties and transformation behaviors of natural bitumen

Natural bitumen is an important component with high-purity organic matter in fossil energy and energy engineering scenarios. However, the production and application of natural bitumen could be severely hindered by the lacking of understanding the effects and influencing mechanisms of original components on physical properties of natural bitumen. Therefore, the main purpose of this work is to illustrate the influence mechanisms of original components (saturated hydrocarbon, aromatic hydrocarbon, resin and asphaltene) on mechanical properties of natural bitumen by the combination of nanoindentation technology and molecular structure analysis. The effects of each original component on the mechanical properties were carried out for Wuerhe natural bitumen which collected from Junggar Basin of China, and the influencing mechanisms were further revealed based on nanoindentation and X-ray diffraction (XRD) results. The occurrence units of each component in the chemical structural stacking of bitumen were established for the first time. It was found that hydrocarbons and resins can disintegrate the chemical structural stacking, thereby reducing the mechanical strength of natural bitumen. According to our micro-scale analysis results, the plastic and elastic deformation of natural bitumen were controlled by the structural units of amorphous carbon and aromatic carbon microcrystalline, as determined by saturated and aromatic hydrocarbons, respectively. And the schematic diagram of occurrence of each component in solid bitumen for the first time. Hence, the mechanical strength of natural bitumen can be effectively reduced by retaining or increasing the content of alkanes during exploitation, transportation and processing of natural bitumen. This research provided a new understanding for the stacking structure and physical property change mechanism of natural bitumen.

Cross-scale mechanical softening of Marcellus shale induced by CO2-water–rock interactions using nanoindentation and accurate grain-based modeling

Mechanical softening behaviors of shale in CO2-water–rock interaction are critical for shale gas exploitation and CO2 sequestration. This work investigated the cross-scale mechanical softening of shale triggered by CO2-water–rock interaction. Initially, the mechanical softening of shale following 30 d of exposure to CO2 and water was assessed at the rock-forming mineral scale using nanoindentation. The mechanical alterations of rock-forming minerals, including quartz, muscovite, chlorite, and kaolinite, were analyzed and compared. Subsequently, an accurate grain-based modeling (AGBM) was proposed to upscale the nanoindentation results. Numerical models were generated based on the real microstructure of shale derived from TESCAN integrated minerals analyzer (TIMA) digital images. Mechanical parameters of shale minerals determined by nanoindentation served as input material properties for AGBMs. Finally, numerical simulations of uniaxial compression tests were conducted to investigate the impact of mineral softening on the macroscopic Young’s modulus and uniaxial compressive strength (UCS) of shale. The results present direct evidence of shale mineral softening during CO2-water–rock interaction and explore its influence on the upscale mechanical properties of shale. This paper offers a microscopic perspective for comprehending CO2-water-shale interactions and contributes to the development of a cross-scale mechanical model for shale.

Atomic layer deposited TiO2 nanofilm on titanium implant for reduced the release of particles.

Objective: Titanium implants are widely used in surgeries for their biocompatibility and mechanical properties. However, excessive titanium particle release can cause implant failure. This study explores Atomic Layer Deposition (ALD) to coat commercially pure titanium (Cp-Ti) with TiO2, aiming to improve its frictional and corrosion resistance while reducing particle release. By comparing TiO2 films with varying ALD cycle numbers, we assess surface properties, particle release, friction, and corrosion performance, providing insights into mitigating particle release from implants. Methods: Cp-Ti surfaces were prepared and coated with TiO2 films of 100, 300, and 500 ALD cycles. Surface characterization involved SEM, EDX, and XRD. Friction was tested using SEM, nanoindentation, and ICP-MS. Corrosion resistance was evaluated through immersion tests and electrochemical analysis. Cytotoxicity was assessed using BMSCs. Results: Surface characterization revealed smoother surfaces with increased ALD cycles, confirming successful TiO2 deposition. Friction testing showed reduced friction coefficients with higher ALD cycles, supported by nanoindentation results. Corrosion resistance improved with increasing ALD cycles, as evidenced by electrochemical tests and reduced titanium release. Cytotoxicity studies showed no significant cytotoxic effects. Conclusion: ALD-coated TiO2 films significantly enhance frictional and corrosion resistance of titanium implants while reducing particle release. The study underscores the importance of ALD cycle numbers in optimizing film performance, offering insights for designing implants with improved properties.

The mechanical properties of Al3Sc single crystal investigated by nanoindentation using Hertzian elasticity theory method and Oliver-Pharr method

The crystal structure, orientation, reduced modulus, and hardness of Al3Sc single crystal were studied using X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and nanoindentation techniques, combined with Hertzian elastic theory method (Hertz) and Oliver-Pharr method (O&P). Millimeter-sized Al3Sc single crystals were prepared using quasi-equilibrium solidification of hypereutectic Al-15(wt %) Sc alloy. The XRD results showed that the samples were composed of L12-Al3Sc and Al phases. The EBSD and nanoindentation results showed that for five Al3Sc single crystals with different orientations, the reduced moduli measured by Hertz method were 146.6 ± 0.4–148.3 ± 0.2 GPa; while measured by O&P method they were 147 ± 2–150 ± 3 GPa. The corresponding hardnesses were varied between 3.8 ± 0.1 and 3.9 ± 0.1 GPa. The Poisson's ratio and elastic constants were determined through iterative calculation based on the relationship between the reduced modulus and Young’s modulus at various orientations. The polycrystal elastic properties, bulk modulus, shear modulus and Young's modulus, were determined. The elastic constants c11, c12, and c44 were 179.2 ± 0.4, 44.1 ± 0.1, and 68.3 ± 0.3 GPa, respectively; the Poisson's ratio was 0.196 ± 0.001. The Young's modulus of five Al3Sc single crystals oriented in different directions was in the narrow range 161–164 GPa. The anisotropy factor of Al3Sc crystal was 1.011 ± 0.002, confirming that it is elastically isotropic. These results provide fundamental information for the research and development of the Al3Sc intermetallic compound and related alloys in future.

Comparative Analysis and Error Assessment of Nanoindentation Evaluation Techniques for NafionTM117

AbstractAdvances in the application of polymers for electrochemical cells require an understanding of their viscous deformation mechanisms and their interaction with moisture. Nanoindentation offers a localized, microscale testing alternative to traditional tensile testing. However, the viscoelastic nature of the polymers, combined with their increased compliance, presents challenges in the analysis of nanoindentation results. In addition, the dependence on moisture results in significant scatter and low repeatability. This study combines nanoindentation and tensile testing as a verification method and compares different correction protocols for static nanoindentation to investigate the mechanical behavior of polymer electrolyte membranes. Comparisons of different indentation devices, analysis methods, and indentation protocols show a significant overestimation of Young’s modulus using the classical Oliver–Pharr method compared to values determined from tensile tests. Nanoindentation at different humidity levels revealed different mechanisms leading to a decrease in Young’s modulus and hardness with increasing humidity.

Influence of the Gas Flow Rate on the Crack Formation of AlCoCrNi High-Entropy Metallic Film Fabricated Using Magnetron Sputtering

In the present study, the AlCoCrNi high-entropy metallic film was deposited on a Si wafer using a magnetron sputtering system. To capture the effects of the sputtering parameters on the microstructure and mechanical properties of the film, the flow rate of Ar gas injected into the chamber (5, 7, and 8 sccm) was controlled. All films were identified as being of BCC phase with compositions of near equiatomic proportions, regardless of the gas flow rates. Nano-scale clusters were observed on the surfaces of all films, and nano-cracks were found in the film deposited at the Ar gas flow rate of 8 sccm, unlike the films deposited at the gas flow rates of 5 and 7 sccm. Detailed microstructural analysis of film deposition at an Ar gas flow rate of 8 sccm indicated that the void boundaries contribute to the formation of nano-cracks. The nano-indentation results indicated that the Ar gas flow rate 5 sccm specimen, with the smallest cluster size at the topmost surface, showed the highest hardness (12.21 ± 1.05 GPa) and Young’s modulus (188.1 ± 11 GPa) values.

Hardening behavior of nickel-base alloy irradiated by multi-energy Fe ions

The multi-energy Fe ions irradiation was performed to avoid the effect of non-uniformity of the ion irradiation damage on the mechanical test of nickel-base alloy (UNS N10003). In this study, the hardening behavior of GH3533 alloy (nickel-base alloy) under the multi-energy Fe ions irradiation at RT and 700 °C was investigated by using nanoindentation, micro-pillar compression techniques, SEM and TEM. The hardness value saturated at 0.5 dpa at RT, according to the nanoindentation results, however the hardness curve sharply rose at the dose of 8 dpa at 700 °C. The plastic deformation curves of the samples at 700 °C had fewer jagged amplitude behaviors and no slip band on the surface, according to the stress-strain curves and in-situ SEM images obtained following the micro-pillar compression test. TEM characterization showed only the dislocation loops and lines were observed at the dose of 8 dpa at RT. However, at 700 °C, precipitates deprived of Fe and Ni and enriched in Mo and Cr were seen close to the dislocation lines at 700 °C. The smooth curves during micro-pillar compression at 700 °C and the abrupt increase in hardness were caused by the high density and uniform dispersion of these precipitates. Additionally, a technique for assessing the hardening behavior under multi-energy ion irradiation was devised, which combines nanoindentation with micro-pillar compression testing.

Study on wear resistance and toughness of calcium ion crosslinked cellulose nanofibers/multi-walled carbon nanotubes/hexagonal boron nitride hybrid reinforced Ni[sbnd]B composite coatings on N80 steel

This study developed a novel NiB/Ca-CNFs/MWCNTs/h-BN coating on N80 steel. The disadvantages of hexagonal boron nitride (h-BN) were improved by creatively combining multi-walled carbon nanotubes (MWCNTs), cellulose nanofibers (CNFs), and calcium ion cross-linking strategies. This led to the creation of Ca-CNFs/MWCNTs/h-BN hybrids, which were then doped into NiB coatings by varying pulse current densities. The results demonstrated that the surface morphology, mechanical properties, and toughness of the composite coating are all influenced by the Ca-CNFs/MWCNTs/h-BN doped at various current densities. Meanwhile, the NiB/Ca-CNFs/MWCNTs/h-BN (4 A/dm2) coating has the greatest microhardness (902.42 Hv) and the smallest friction coefficient (0.487) under reciprocating dry sliding friction conditions of Si3N4 friction balls. In addition, the results of nanoindentation and tensile tests show that the elastic modulus of NiB/Ca-CNFs/MWCNTs/h-BN (4 A/dm2) composite coating is 194.096 MPa and the tensile elongation is 12.2 %.

A novel CrCx/C-Cr multilayer PVD coating for cotton picking spindle: committed to replacing traditional electroplated chromium coating

A novel CrCx/C-Cr multilayer coating for cotton picking spindles was prepared on a 20CrMnTi substrate using PVD technology. Compared to the traditional electroplated chromium coating, the CrCx/C-Cr coating has a dense structure, and no micro-cracks were observed on the surface. The results of nanoindentation show that the nano-hardness of the CrCx/C-Cr coating is about 8.46 GPa, which is 78.5% higher than that of the substrate. Additionally, the CrCx/C-Cr coating has a lower friction coefficient and wear rate compared to the electroplated chromium coating, indicating better wear resistance properties. The multilayer CrCx/C-Cr coating is expected to replace the high-pollution chromium coating for cotton picking spindles.

Investigation of silicon carbon oxynitride thin film deposited by RF magnetron sputtering

In this research, silicon carbon oxynitride (SiCON) thin films were deposited on silicon substrate by a radio frequency magnetron sputtering method. The effect of methane reactive gas flow rate on the structural, morphological, optical, and mechanical properties of the thin films was evaluated by using of grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) , field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), fourier transform infrared spectroscopy (FTIR), ellipsometry and nano-indentation methods. The results of the GIXRD proved the formation of an amorphous structure in the thin films. Also, the Raman spectroscopy results determined the absence of graphite nanocrystals in the thin film structure. FE-SEM revealed the formation of a thin film with a smooth, dense and crack-free surface. AFM results showed that SiCON thin film is formed with very low surface roughness in the RMS range of 0.73 nm to 4.39 nm. The results of the ellipsometry analysis indicated that the refractive index of the thin film was changed during increase of the CH4 reactive gas flow rate in the of 1.4 to 1.61 at 4 µm. According to the nano-indentation results, sample N10-C20-R1 has the highest hardness and Young's modulus equals 22.7 GPa and 231.6 GPa, respectively.

Crystallization kinetics and nanoindentation studies of Cu46Zr40Ti8.5Al5.5 glassy alloy

Crystallization kinetics of Cu46Zr40Ti8.5Al5.5 metallic glass is investigated in non-isothermal and isothermal conditions. In non-isothermal condition, the crystallization activation energy is determined using Kissinger's method. Further, activation energy of reported Cu-Zr-Al metallic glasses are compared with Cu46Zr40Ti8.5Al5.5 alloy to understand the effect of Ti addition on crystallization kinetics. Detailed investigation on activation energy through the crystallization process is studied. To understand the influence of nucleation and growth mechanism during the crystallization steps, samples are heated in isothermal conditions at various annealing temperatures in supercooled liquid region to determine the local Avrami's exponent using Johnson-Mehl-Avrami equation. Additionally, small scale mechanical response is noted on metallic glass sample to determine the influence of structure on hardness and elastic modulus. Nanoindentation results showed hardness value of 5.39 ± 0.09 GPa and Young's modulus of 92.81± 0.52 GPa.

A temperature-based synthesis and characterization study of aluminum-incorporated diamond-like carbon thin films

The present work deals with the study of various properties of aluminum (Al)-incorporated diamond-like carbon (DLC) thin films synthesized using the atmospheric pressure chemical vapor deposition (APCVD) technique by varying the deposition temperature (Td) and keeping the N2 flow rate constant. Surface morphology analysis, resistance to corrosion, nanohardness (H), and Young’s modulus (E) of the coatings were carried out using atomic force microscopy (AFM), corrosion test, scanning electron microscopy (SEM), and nanoindentation test, respectively. SEM results showed a smoother surface morphology of the coatings grown at different process temperatures. With an increase in process temperature, the coating roughness (Ra) lies in the range of 20–36 µm. The corrosion resistance of the coating was found to be reduced with a consecutive increase in the deposition temperature from 800℃ to 880℃. However, above 880℃, the resistance increases further, and it may be due to the presence of more Al weight percentage in the coating. The nanoindentation result revealed that H and E of the coating increase with an increase in the CVD process temperature. The elastic–plastic property indicated by H/E and H3/E2, which are also indicators of the wear properties of the coating, were studied using the nanoindentation technique. The residual stresses (σ) calculated using Stoney’s equation revealed a reduction in residual stress with an increase in the process temperature.