Thermal Stability Of Microstructure Research Articles

Enhancing Ω Phase Thermal Stability in Al Alloys through Interstitial Ordering.

Scandium (Sc) can orderly occupy interstitial sites within the Ω phase of aluminum alloys, forming a new phase that significantly enhances the thermal stability of the alloy. However, Sc is relatively expensive and rare. In this work, we employ first-principles calculations to delve into the physical essence interstitial ordering of Sc in enhancing thermal stability at the electronic level, thereby revealing the crucial factors responsible for this improvement. By computationally screening all potential metallic elements across the periodic table, we uncover that, in addition to Sc, a diverse range of elements including lithium (Li), calcium (Ca), strontium (Sr), and some of rare earth elements (Sm, Ce, Y), possess the potential to contribute to thermal stability enhancement through interstitial ordering mechanisms in aluminum alloys. This study deepens our understanding of microstructural thermal stability and offers novel strategies for designing improved thermally stable Al alloys.

Enhancing Ω Phase Thermal Stability in Al Alloys through Interstitial Ordering.

Scandium (Sc) can orderly occupy interstitial sites within the Ω phase of aluminum alloys, forming a new phase that significantly enhances the thermal stability of the alloy. However, Sc is relatively expensive and rare. In this work, we employ first-principles calculations to delve into the physical essence interstitial ordering of Sc in enhancing thermal stability at the electronic level, thereby revealing the crucial factors responsible for this improvement. By computationally screening all potential metallic elements across the periodic table, we uncover that, in addition to Sc, a diverse range of elements including lithium (Li), calcium (Ca), strontium (Sr), and some of rare earth elements (Sm, Ce, Y), possess the potential to contribute to thermal stability enhancement through interstitial ordering mechanisms in aluminum alloys. This study deepens our understanding of microstructural thermal stability and offers novel strategies for designing improved thermally stable Al alloys.

Thermal stability of microstructure on heat treatment of friction stir welded AA2014-T651 aluminum joints

Исследовано влияние термической обработки на микроструктуру и механические свойства соединений из алюминиевого сплава AA2014-T651, полученных сваркой трением с перемешиванием. Сварка трением с перемешиванием выполняется с помощью треугольного инструмента при двух скоростях вращения: 1000 и 1400 об/мин. При этом сварка осуществлялась с постоянной скоростью 63 мм/мин при обеих скоростях вращения инструмента. Установлено, что сварка трением с перемешиванием приводит к значительному измельчению микроструктуры и частичному растворению упрочняющих включений. Сварные соединения подвергали термообработке при температурах 573, 673, 773 и 823 К в течение одного часа. При термообработке наблюдалось вторичное выделение и укрупнение включений в сварном шве. Показано, что увеличение скорости вращения инструмента значительно повышает термическую стабильность микроструктуры, практически не вызывая аномальный рост зерен в сварном шве.

Thermal stability of microstructure and properties of ingots and fine wires from Al–Zr alloys

The process of precipitation of Al3Zr particles in cast Al–(0.25–0.4) wt % Zr alloys manufactured by the induction casting method is studied. The effect of zirconium concentration on the microstructural parameters, hardness, and specific electrical resistance (SER) of cast alloys is investigated. The dependences of hardness and SER on the time of cast alloys annealing at 500°C are plotted. The parameters of the Johnson–Mehl–Avrami–Kolmogorov equation for alloys with different Zr content are determined. The optimal regimes of cast ingot aging are found. Fine wires with ∅ 0.3 mm are manufactured by the drawing method; their strength, SER, and hardness are studied in the initial state and after heat treatment. The tests of thermal stability of wires are carried out according to the state standard GOST R MEK 62004–2014.

Thermal Stability of Residual Stress, Microstructure, and Mechanical Property in Shot-Peened CNT/Al-Cu-Mg Composites

To investigate the thermal stability of a shot-peened specimen and ensure the reliability operation under high temperatures, CNT/Al-Cu-Mg composites were treated by shot peening (SP) and the isothermal aging treatment. The heating temperatures were 100, 150, 200, and 250 °C. Changes in surface residual stress and the distribution along the depth were investigated. The microstructure changes were analyzed by XRD and observed by TEM. Changes in mechanical properties were characterized by microhardness. The results show that the compressive residual stress (CRS) release and the microstructure changes mainly occurred at the initial stage of heating treatment. After 128 min of isothermal aging treatment at 250 °C, the surface CRS released 91.9% and the maximum CRS released 80.9%, the surface domain size increased by 222%, and the microstrain and microhardness decreased by 49% and 27.3%, respectively. The reinforcement effect introduced by SP basically disappeared. A large number of second-phase particles, such as CNT, Al2Cu, and Al4C3, were anchored at grain boundaries, hindering dislocation movement and enhancing the thermal stability of the material. Isothermal aging treatment at 100 °C and 150 °C for a duration of 32 min is a reliable circumstance for maintaining SP reinforcement.

Developing a high-speed-extruded BMZQ5100 alloy with higher strength and microstructural thermal stability than AZ91 alloy

A new Mg-5Bi-1Mn-0.5Zn-0.2Ag (BMZQ5100, wt%) alloy is developed and analyzed comparatively its extrudability, microstructure, mechanical property and thermal stability with a commercial AZ91 alloy. The results show that the BMZQ5100 alloy can be successfully extruded at a high extrusion speed (ES) of 30 m/min without surface cracks, but there are a large number of hot cracks occurred on the low-speed-extruded AZ91 alloy surface (ES: 5 m/min). For the 30 m/min extruded BMZQ5100 alloy (BMZQ5100-E30), it exhibits a completely dynamic recrystallized (DRX) grain structure with a slightly larger grain size and stronger basal fiber texture than the 2 m/min extruded AZ91 alloy (AZ91-E2) without surface cracks. In terms of second phase, the former alloy contains submicron Mg3Bi2 phases at grain boundaries (GBs), nano-scale Mg3Bi2 and α-Mn particles within grain interiors, along with the co-segregation of Zn and Ag at GBs. The latter alloy has a continuous network of submicron Mg17Al12 phases along GBs, but no any solute segregation is observed at GBs. The BMZQ5100-E30 alloy exhibits more excellent mechanical properties with a tensile yield strength of ∼ 271 MPa, an ultimate tensile strength of ∼ 319 MPa and an acceptable elongation-to-failure of ∼ 8%, compared with the AZ91-E2 alloy. The GB strengthening, precipitation strengthening and solute segregation strengthening on the TYS occupy ∼ 46.2, ∼ 45.5 and ∼ 8.3%, respectively. In addition, the BMZQ5100-E30 alloy has higher microstructural thermal stability than the AZ91-E2 alloy, because of second phase pinning and solute segregation at GBs to effectively inhibit the grain growth during annealing.

The mechanical property and microstructural thermal stability of gradient-microstructured nanotwinned copper films electrodeposited on the highly (111)-orientated substrates

Three different substrates with varying (111) textures were used to study the epitaxial growth behavior of nanotwinned copper (nt-Cu) films during direct current electroplating. The (111) proportions for substrates are 78.5%, 97.5%, and 100%, while for the electrodeposits they are 69.3%, 92.7%, and 98.3%, showing a positive correlation between the (111) proportions of the substrates and the electrodeposits. Secondary ion microscopy (SIM) reveals a transition layer consisting of fine grains forms between the columnar nanotwinned grains region and the substrate, exhibiting a gradient microstructure within the nt-Cu films. The thickness of the transition layer shows a reducing tendency as the (111) proportion of substrate increases. Furthermore, to investigate the mechanical properties of the transition layer, a nano-indentation test was performed on the cross-section of gradient-microstructured films. The average hardness of the transition layer near the substrate is 3–4 GPa, which is approximately two times higher than that of the columnar nanotwinned region. The excellent hardness is probably induced by the decrease in grain size and the presence of high-density twin boundaries within the grains. An in-situ annealing test at 300 °C was performed on these three electrodeposits to assess their microstructural thermal stability. It is noticed that the thickness of transition layer would affect the competition of grain growth between substrate grains and columnar nanotwinned grains during aging. Higher microstructural thermal stability could be achieved with fewer grains in the transition layer. Overall, this study reveals the high mechanical properties and microstructural thermal stability of the transition layer, which should be helpful in understanding and promoting the application of nt-Cu thin films.

Influence of Thermomechanical Treatment Mode on Thermal Stability of Microstructure, Mechanical Properties, and Fracture Features of V–Cr–W–Zr Alloy

Influence of Thermomechanical Treatment Mode on Thermal Stability of Microstructure, Mechanical Properties, and Fracture Features of V–Cr–W–Zr Alloy

Thermal stability of Ni3Al microstructure and microhardness after spark plasma sintering

The effect of high-temperature annealing on the structural-phase state and microhardness of Ni3Al samples obtained by spark plasma sintering after high-energy ball milling has been studied. Using X-ray diffraction analysis, scanning and transmission electron microscopy, a comparative study of the features of the structural-phase state of Ni3Al samples depending on the duration of preliminary high-energy ball milling and annealing temperature was carried out. Temperatures have been identified that ensure simultaneous grain growth at a high density of nuclei, which contributes to the formation of a fine-grained structural state. Depending on the state of the material, the corresponding microhardness values have been determined. The influence of the annealing temperature on the strengthening mechanisms has been analyzed.

Thermal stability of microstructure and corresponding hardness variations in two high-carbon nanostructured bainitic steels

The autotempering phenomenon and carbon partitioning from bainitic subunits during the bainite transformation suggest that the tempering behavior of the nanostructured bainite may be different compared to that of martensite. This article aims to investigate the thermal stability of the microstructure in two low alloy nanostructured bainitic steels containing 0.89 wt% carbon content. Nanostructured bainite was obtained after austempering at 250 °C for optimum heat treatment time. Nanostructured bainitic steels were tempered at the temperature range of 300–700 °C for 30 min. Additionally, the effect of prolonged austempering beyond the optimum heat treatment condition at austempering temperature was studied. Microstructural characteristics were evaluated using optical and field emission gun scanning electron microscopes and X-ray diffraction methods. Hardness variations during tempering of nanostructured bainite compared with that of martensite microstructure obtained in the same primary steels after austenitizing and quenching. Results indicated that microstructural characteristics of nanostructure bainite didn’t change significantly at heat treatment times longer than that needed for bainite transformation completion at isothermal bainite heat treatment temperature. Moreover, results approved the higher tempering resistance of nanostructured bainite compared to that of martensite in the same steel. It has been shown that tempering the nanostructured bainite up to 400 °C didn’t change the microstructure and hardness, while the changes were pronounced at higher tempering temperatures. It has been suggested that cementite precipitation was more significant when a higher number of dislocations were present in nanostructured bainite before starting the tempering process.

Thermal stability of the Cr-coated zirconium alloy microstructure prepared by pulsed laser deposition

Thermal stability of the Cr-coated zirconium alloy microstructure prepared by pulsed laser deposition

Thermal stability of microstructure and their influences on mechanical properties of precipitation-hardened medium-entropy alloy Ni43.4Co25.3Cr25.3Al3Ti3

The thermal stability of the coherent, nanoscale, L12 precipitates and fine grains in a strong, ductile medium-entropy alloy (MEA) Ni43.4Co25.3Cr25.3Al3Ti3 were analyzed and related to the room-temperature mechanical properties. Increasing the aging temperature and prolonging the soaking time produced more L12 precipitates and reduced the matrix lattice constant. The fine grains exhibit excellent thermal stability with a very low coarsening rate (1.73 × 10−24 m3/s at 700 °C, 4.78 × 10−23 m3/s at 800 °C, and 4.32 × 10−22 m3/s at 900 °C), which mainly results from the strong pinning from the high density of precipitates and high activation energy for grain growth (∼272 kJ/mol). The L12 precipitates remain spherical and have a coherent relationship with the matrix during ripening from tens to hundreds of nanometers. They exhibit better thermal stability (6.45 × 10−30 m3/s at 700 °C, 2.03 × 10−28 m3/s at 800 °C, and 7.16 × 10−27 m3/s at 900 °C) than the L12 precipitates in nickel-based superalloys by 1–2 orders of magnitude with an activation energy of 341 kJ/mol. The critical size for the transition from dislocation shear of the L12 precipitates to dislocation looping is 23.5–30.4 nm. No significant coarsening of either the grain size or L12 precipitates caused a small decrease in the YS and UTS of MEA aged at 700 °C. In comparison, both the YS and UTS of MEA aged at 800–900 °C dramatically decreased, which is caused by the coarsening of the L12 nanoparticles and the average grain size. This decrease in strength was accompanied by a slight increase in ductility at all three aging temperatures.

Realizing impressive superplasticity in a low-alloyed Mg-Zn-Ca-Al-Mn alloy: The roles of grain boundary segregation and dense β-Mn particles

Achieving impressive superplasticity is an important strategy to manufacture Mg alloy products with complex shapes. In the present study, we report that an excellent superplastic deformation with elongation larger than 500% can be achieved at 623 K and 1.0 × 10−3s−1 in a Mg-1.51Zn-0.59Ca-0.59Al-0.70Mn (wt.%, ZXAM2111) alloy fabricated by equal-channel angular pressing. The superplastic deformation is mainly carried by grain boundary sliding (GBS), accompanied by a grain size growth from ∼3.0 µm to ∼6.0 µm after deformation. Before deformation, the ZXAM2111 alloy is mainly characterized by a strong co-segregation of Zn and Ca atoms at grain boundaries and uniformly distributed β-Mn particles. With deformation proceeding, the β-Mn particles further dynamically precipitate along grain boundaries that parallel the tensile axis, leading to improved resistance to grain coarsening. Although the enhanced stabilizing effects decrease the strain rate sensitivity value, the resulting impressive microstructure stability provides a cornerstone of the active operation of GBS, facilitating the achievement of superplastic deformation. The present work could provide insight into developing low-alloyed Mg alloys with high microstructure thermal stability to achieve superplasticity.

Thermal stability of laser track microstructures in an Al-Cr-Co-Mn-Zr I-phase alloy

Laser glazing of solid metal surfaces is an efficient and cost-effective way to evaluate the potential of an alloy system for use in metal additive manufacturing (MAM), but there are concerns about the stability of the resulting microstructures. Here it is shown that in situ transmission electron microscopy heating experiments on specimens cut from laser glazing tracks using focused ion beam methods can provide a useful insight into the transformation phenomena that occur upon reheating. Examples of such experiments are presented for laser tracks in a powder-processed Al-Cr-Mn-Co-Zr alloy, which contains a complex distribution of icosahedral quasicrystal (I-phase) dispersoids in a polycrystalline FCC Al matrix. Initial ramped heating experiments were performed to identify suitable conditions for isothermal studies of transformation pathways. Tracks with the lowest laser energy input exhibited supersaturated solid solution microstructures. These were stable during ramped heating to around 375 °C. For isothermal exposures at 400 °C there was precipitation of Al4(Cr,Mn) both at grain boundaries and within the FCC Al matrix phase. In tracks with higher laser energy input, equiaxed I-phase dispersoids were formed in the matrix. These microstructures were stable during ramped heating to around 400 °C. In isothermal experiments at 425 °C, there was precipitation of Al4(Cr,Mn), followed by the onset of I-phase decomposition. The partially decomposed dispersoids exhibited an I-phase core surrounded by a shell of Al45(Cr,Mn)7. In isothermal experiments at 450 °C, the dispersoids decomposed completely to form Al4(Cr,Mn), indicating that Al45(Cr,Mn)7 is a metastable intermediate transformation product. These observations provide a useful guide to the transformations that might occur during MAM processing of this alloy system.

Effect of Er, Si, Hf and Nb Additives on the Thermal Stability of Microstructure, Electrical Resistivity and Microhardness of Fine-Grained Aluminum Alloys of Al-0.25%Zr.

The conductor aluminum alloys of Al-0.25wt.%Zr alloyed additionally with X = Er, Si, Hf and Nb were the objects of our investigations. The fine-grained microstructure in the alloys was formed via equal channel angular pressing and rotary swaging. The thermal stability of the microstructure, specific electrical resistivity and microhardness of the novel conductor aluminum alloys were investigated. The mechanisms of nucleation of the Al3(Zr, X) secondary particles during annealing the fine-grained aluminum alloys were determined using the Jones-Mehl-Avrami-Kolmogorov equation. Using the Zener equation, the dependencies of the average secondary particle sizes on the annealing time were obtained on the base of the analysis of the data on the grain growth in the aluminum alloys. The secondary particle nucleation during long-time low-temperature annealing (300 °C, 1000 h) was shown to go preferentially at the cores of the lattice dislocations. The Al-0.25%Zr-0.25%Er-0.20%Hf-0.15%Si alloy subjected to long-time annealing at 300 °C has the optimal combination of microhardness and electrical conductivity (59.8%IACS, Hv = 480 ± 15 MPa).

Sc/Zr ratio-dependent mechanisms of strength evolution and microstructural thermal stability of multi-scale hetero-structured Al–Mg–Sc–Zr alloys

• A tensile strength of ∼605 MPa and ∼10% elongation were obtained in Al–7Mg–0.3Sc–0.1Zr. • The strength-ductility synergy owes to a multi-scale heterogeneous microstructure. • While Al–7Mg–0.1Sc–0.3Zr had higher thermal stability at ≥ 400 °C than high-Sc/Zr ratio alloys. • High-content Zr atoms are helpful in enhancing precipitation and coarsening resistance of Al 3 (Sc,Zr). Microstructure and its thermal stability are critical in the development of high-performance Al–Mg alloys. Here, we attempt to tailor Al 3 (Sc,Zr) precipitates and thus microstructure characteristics to manipulate mechanical properties and microstructural stability of Al–7Mg alloys fabricated by hot extrusion combined with two-pass hard-plate rolling via changing Sc/Zr ratio. Increasing Sc/Zr ratio leads to improved strength without any loss of ductility. A strength-ductility synergy, i.e. yield strength of ∼548 MPa and ultimate tensile strength of ∼605 MPa with an impressive ductility of ∼10% elongation was achieved in the Al–7Mg–0.3Sc–0.1Zr alloy. The good strength-ductility synergy is ascribed to the multi-scale heterogeneous microstructure promoted by the high Sc/Zr ratio, i.e. a bimodal grain structure, profuse low angle grain boundaries, dispersed nano-sized Al 3 (Sc,Zr) precipitates coexisting with intragranular Mg-Zr co-clusters segregated at dislocations. Upon thermal exposure, the Al–7Mg–0.3Sc–0.1Zr alloy maintained higher hardness at below 250 °C, whereas Al–7Mg–0.2Sc–0.2Zr and Al–7Mg–0.1Sc–0.3Zr alloys exhibited higher hardness in moderate- and high-temperature range of 250-350 °C and ≥ 400 °C, respectively. Atom-probe tomography analysis illustrates that slow-diffusing Zr atoms enhance Al 3 (Sc,Zr) coarsening resistance through forming a higher-content Zr-enriched protective shell around a Sc-enriched core in Al–7Mg–0.1Sc–0.3Zr. Meanwhile, the high Zr content promotes concurrent Al 3 (Sc,Zr) precipitation during thermal exposure at high temperatures. The improved microstructural thermal stability in Al–7Mg–0.1Sc–0.3Zr alloy is further discussed in terms of the recrystallization resistance and grain growth behavior. The present study reveals the feasibility for designing high-strength and thermally stable hetero-structured Al–Mg–Sc–Zr alloys via tailoring Sc/Zr ratios for different application temperature ranges.

Enhancing high-temperature tensile properties of Ni/Ni-W laminated composites for MEMS devices

There is an increasing demand for materials with excellent mechanical performance for Micro-Electro-Mechanical System (MEMS) devices serving at elevated temperatures. However, how to enhance the high-temperature strength of the materials without losing their plasticity is a pending problem. Here, the Ni/Ni-W laminated composites with different monolayer thicknesses and the same ratio of the constituent layer thicknesses were fabricated successfully by using the dual-bath electrodeposition technique. The microstructure stability and tensile properties of annealed Ni/Ni-W laminated composites with different monolayer thicknesses were investigated at 400 °C. The results show that the annealed Ni0.5/Ni-W0.05 laminated composites have both high yield strength (450 MPa) and excellent elongation to failure (25.1%) at 400 °C, being superior to that of the monotonic Ni (179 MPa and 17.7%). Such a high strength of the laminated composite at 400 °C results from the contribution of the intrinsically high strength of the Ni-W layers with excellent thermal stability, the thickness-constrained effect on grain growth of Ni layers and the interface coupling effect of heterogeneous structures. The good plasticity may be derived from the heterogeneous laminated structure and the decrease in the constituent layer thickness, providing a good co-deformation ability. Basic mechanisms for the high tensile strength and good plasticity of the Ni/Ni-W laminated composites at 400 °C were analyzed theoretically. The findings reveal a potential strategy to fabricate MEMS components with excellent high-temperature tensile properties through tailoring the microstructure thermal stability and the constituent layer scale.

Zirconium tungstate reinforced energetic composites with inhibited thermal expansion and reduced thermal stress

Due to their large positive thermal expansion property, polymer bonded explosives (PBXs) are prone to deform under environmental temperature cycle. Based on the volume compensation effect, zirconium tungstate (ZrW2O8) with a negative thermal expansion (NTE) characteristic was first introduced to tailor the thermal expansion of energetic composites in this work. The PBXs modified with ZrW2O8 were fabricated by non-water kneading granulation technique, and their thermal expansion, mechanical properties, as well as microstructural thermal stability were systematically investigated. The coefficient of thermal expansion (CTE) during the heating stage and the strain were reduced by 19.8% and 19.1% for modified PBXs with the incorporation of 10 wt% ZrW2O8. For ZrW2O8 filled energetic composites at lower filler loading (≤10 wt%), the experimental values fell in between the Turner’s model and Schapery’s lower boundaries. Numerical simulation revealed that the decreased CTE could reduce thermal stress, which would benefit the safety and reliability of the weapon system. Combined with thermal and mechanical analyses, the thermal shock resistance of the ZrW2O8 modified energetic composite with 10 wt% filler loading was found to be 45% higher than that of pristine PBX without ZrW2O8, suggesting a reinforcement effect, which would be helpful for long-term storage of materials under environmental temperature cycles. The successful application of this functional NTE system to energetic materials might provide a new strategy for the construction of novel energetic composites with tailored thermal expansion.

Особенности формирования микроструктуры алюминиевых сплавов АК4-1 и АК12Д после их совместной обработки трением с перемешиванием

Friction stir processing is one of the modern methods of local modification of the surface of aluminum alloys in the solid-phase state, which provides the dispersion of structural components. In heat-hardened aluminum alloys with a matrix type structure, heat treatment following after friction stir processing can lead to abnormal grain growth in the stir zone. However, in alloys with the structure close to microduplex type, a fine-grained structure can be formed after friction stir processing and heat treatment. This work is aimed at evaluating the possibility of increasing the microstructure thermal stability of the AK4-1 (Al–Cu–Mg–Fe–Si–Ni) matrix-type aluminum alloy. For this purpose, AK12D (Al–Si–Cu–Ni–Mg) aluminum alloy with the structure close to microduplex type was locally mixed into the studied alloy by friction stir processing. Subsequent Т6 heat treatment was carried out according to the standard mode for the AK4-1 alloy. Studies showed that the stir zone had an elliptical shape with an onion-ring structure. This structure comprised alternating rings with different amounts and sizes of excess phases. At the same time, in the stir zone center, the width of rings and the average area of excess phases were larger compared to the stir zone periphery, where the width of rings and the average area of particles were smaller. The average area of excess phases in the rings with their higher content was smaller than in the rings with their lower content. This distribution of excess phases leads to the formation of a fine-grained microstructure, where the average size of grains depends on the interparticle distance in the α-Al solid solution.

Investigating the effect of bias voltage on the microstructural thermal stability and tribological performance of N-doped hydrogenated diamond-like carbon coatings

Here, N-doped hydrogenated diamond-like carbon (a-C:H:N) coatings were deposited onto 316 L stainless steel and silicon wafer substrates by applying plasma-enhanced chemical vapor deposition at different bias voltages (Vb). The coatings were annealed at 25–590 °C for 4 h. The structure and chemical bonding of the coatings were characterized using scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The residual stress, surface hardness, and tribological performance were investigated by using the Stoney method, a nanoindenter, and sliding against alumina. The fraction of the constituent bonds in the coating was controlled depending on Vb. The evolution of these bonds during annealing determined the thermal and mechanical performance of the a-C:H:N coatings, particularly the CHn group, sp2C bonds, and CO bonds (CO and CO). As Vb increased, the fraction of CHn groups, CO bonds, and CN bonds decreased, whereas that of sp2C increased. When annealed at above 430 °C, the breakage of the CHn groups and CN bonds accelerated the sp3 → sp2 transformation. The coating prepared at −500 V exhibited the highest hardness of 22.5 GPa and low residual stress of −0.57 GPa; after annealing at 590 °C for 4 h, a hardness of 15 GPa was maintained. The wear resistance was positively related to the surface hardness of the coatings, whereas the coefficient of friction was responsible for the fraction of sp3CHn, CO bonds, and sp2C bonds. The wear resistance of the coating deposited at −500 V was double that of the coating deposited at −740 V.