Wear Test Conditions Research Articles

Tribological Behavior and Mechanism of Plasma-Sprayed High-Entropy Monoboride Coating over a Wide Temperature Range

Due to the extremely high hardness of high-entropy monoborides (HEMB), this study successfully prepared a new type of HEMB-(V0.2Cr0.2Ta0.2Mo0.2W0.2)B coating by adjusting the spraying process using atmospheric plasma spraying technology. The high-entropy coating was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The change rule concerning the alteration in the phase composition of the coating surface with power and protective atmosphere was explored, indicating that with the decrease in power and the application of a protective atmosphere, the generation of oxide on the coating surface is successfully inhibited. The wear resistance of the coating in a temperature range from room temperature to 800 °C was evaluated in dry sliding wear test conditions. The results indicated that the wear mechanism of (V0.2Cr0.2Ta0.2Mo0.2W0.2)B coating below 400 °C is abrasive wear, and above 400 °C, the wear mechanism is mainly oxidative wear.

Investigation of Tribological Behavior of PTFE Composites Reinforced with Bronze Particles by Taguchi Method

Reinforced PTFE materials can be designed to show high mechanical stability against harder materials under sliding wear conditions. Especially bearing metal-reinforced PTFE is of high practical interest. In this class of materials, bronze-filled PTFE was reported to obtain high wear resistance, a low coefficient of friction (COF), and excellent self-lubrication properties in sliding conditions. In the statistical approach of this work, PTFE composites reinforced with 25 vol%, 40 vol%, and 60 vol% bronze particles were evaluated against pure PTFE regarding wear behavior under varied wear test parameters, i.e., material, normal load, and sliding speed. Wear tests were planned to use a standard orthogonal array based on the Taguchi design method. An analysis of variance test was utilized to quantify the effects of test parameters on the wear behavior of the bronze/PTFE composites and pure PTFE. According to the variance analysis, the material type has the largest influence on the COF and the specific wear rate (SWR) under test conditions of this work. Both COF and SWR were found to be influenced by the material type (29.83% and 96.16%), the normal load (33.34% and 0.95%), and sliding speed (9.14% and 1.28%). The lowest SWR and COF values were achieved at the optimum wear test conditions where the wear test parameters were 1 m/s sliding speed (A4B2C2) at PTFE + 60 vol.% bronze reinforced composite 50 N application load and 0.32 m/s sliding speed (A4B3C1) at PTFE + 60 vol.% bronze reinforced composite 100 N application load, respectively.

Determination of the construction material for phononic band gap structures by tribological performance

This study investigates the tribological performances of commonly used stainless steel alloys (303, 304, 316L, and 420) to determine their suitability as construction materials for periodic structures designed for inertial amplification induced phononic band gap vibration isolators. Stainless steel alloys are extensively employed in engineering structures due to their ability to withstand large stresses and exhibit excellent cyclic loading properties. In this study, stainless steel specimens are examined by dry and lubricated wear test conditions. 420 stainless steel showed highest wear resistant properties for dry and lubricated conditions. Two grades of lubricants are compared in terms of viscosities, and it is revealed that higher viscosity blocked the flow of the lubricant so that semi-dry friction occurred. Low viscosity lubricant enabled less material removal due to friction.

Development and evaluation of CrAlAgN self-lubricating coatings for high temperature metal forming dies

Conventional lubricants are widely used for die release as well as for cooling assistance on the die surface. However, lubrication is difficult at high temperatures. Oxidation and scaling occur on the work pieces that lead to poor surface finish and a possible warping of the material during cooling. The aim of this research is to develop self-lubricating CrAlAgN nanocomposite coatings for metal forming dies and evaluate their thermal fatigue resistance and wear behavior at elevated temperatures. The CrAlAgN coatings with different Ag contents have been deposited by plasma-enhanced magnetron sputtering. The structure and properties of the coatings were systematically studied to determine the optimal Ag content for achieving a combination of good adhesion, thermal fatigue resistance, and surface lubricity at elevated temperatures. The thermal fatigue resistance of the coatings was evaluated using thermal cyclic testing by cycling the coatings from room temperature to 800 °C up to 1200 cycles. The high temperature wear behavior of the coatings was evaluated using a tribometer up to 900 °C. Good thermal fatigue resistance and low coefficient of friction (COF) were observed in the CrAlAgN coatings with an Ag content in the range of 5–10 at. % at 800 °C. The CrAlAgN coating with 10 at. % Ag exhibited the lowest average COF of 0.05 at 800 °C. The COF of thick CrAlAgN coatings (8 at. % Ag) decreased from 0.5 to 0.2 from 500 to 900 °C, accompanied by an increase in the wear rate under more aggressive wear test conditions. The lubricity of the CrAlAgN coatings at high temperatures was attributed to the lubrication effects from the mixed oxides and encapsulated Ag diffused toward the surface. To further evaluate the coating performance, a hydraulic hot forging punch was coated with a thick CrAlAgN (8 at. % Ag) coating and evaluated in the industrial forging process. The preliminary in-plant trials demonstrated that the coating significantly reduced the dimensional distortion and wear for the forging punch.

Evaluation of physical, mechanical and sliding wear properties of in-situ AB-TiC composite: a comparison with NAB alloy

The purpose of the present study is to evaluate the physical, mechanical and sliding wear properties/response of cast in-situ aluminium bronze (AB)-TiC [(Cu10Al3Fe)5TiC] composite and compare with cast nickel aluminium bronze (NAB) [Cu10Al5Ni5Fe] alloy. Sliding wear tests were conducted in dry and partially lubricant conditions using a pin-on-disc machine. A test material in the form of pin was evaluated against a rotating heat-treated EN-31 steel disc. Wear loss, frictional heating and friction coefficient properties were examined. The NAB alloy showed higher tensile strength (32.7%), compressive strength (7.68% at room temperature. and 4.18% at 500 °C), hardness (8.78%) and density (3.17%), whereas thermal conductivity of the AB-TiC composite was found 4.89% higher than NAB alloy. In dry sliding condition, composite outperformed NAB alloy in terms of wear resistance up to a critical applied load and/or sliding speed. Beyond this point, the wear behavior altered. Increasing sliding speed caused to reduce wear transition load. While friction coefficient showed mixed trend. Under lubricated wear test conditions, AB-TiC composite displayed considerably higher wear resistance (50.08%, 44.41% & 51.55%) and friction coefficient (26.37%, 40.75% & 14.96%) than the NAB alloy when tested in only oil, oil with 100 μm graphite and oil with 7–10 μm graphite respectively. Arrival of seizure in general caused significantly higher wear loss and temperature rise. In addition, it caused large adhesion of the specimen material to the disc surface. The reported wear behaviour of the samples has been validated using the features of wear surfaces and subsurface regions. The latter also permitted to comprehend the working wear processes. The analysis significantly shows good impacts of the oil lubrication (with and without solid particles) in terms of decreasing wear rate, frictional heating, and friction coefficient. Formation of steady lubricating film/layer was reported to be responsible for the better wear performance of the samples. Furthermore, irrespective of material composition and microstructure there exists a precise set of test parameters (e.g. load and speed) leading to optimal wear performance wherein the beneficial impacts of load bearing capability, thermal stability of various phases predominates.

Microstructure and Wear Resistance in Medium and High C Steels Treated by Quenching and Partitioning

The quenching and partitioning (Q&P) steels have shown to be promising candidates to be applied in fields where wear resistance is required. In this study, a medium and a high C steel are heat treated by Q&P and the resulting microstructure, hardness, and wear resistance are characterized. The mechanical stability of the austenite phase under wear test conditions is investigated. It is found that the stability of austenite is very high in the high C steel and decreases in the medium C steel. Additionally, the hardness and wear behavior of the Q&P‐treated steels are compared with the results obtained for quenching and tempering (Q&T) treated samples, showing that, although the hardness of Q&P steels is quite lower, the obtained wear rates are similar. It means that in the studied Q&P steels, although the austenite transformation into martensite does not occur considerably, the presence of austenite might play a key role in the wear resistance.

Effect of buttering on the wear behavior of the SMA welded hardfacing layer in a low-carbon steel

Abstract In this study, the effect of the buttering layer (18.5% Cr + 9% Ni) and the chemical composition of the hardfacing filler materials on the microstructure and wear behavior of the structural steel (S355JR) was investigated. The chromium-based hardfacing alloys deposited by shielded metal arc welding (SMAW) have also been investigated to establish the relationship between microstructures and wear properties. The microstructure of hardfacing deposits has been examined by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. A linear reciprocating abrasive wear test experiment was conducted on the hardfacing deposits using an Al2O3 ball under constant wear test conditions. The experimental results show that the microstructure of hardfacing deposits consists of martensitic matrix and complex (M7C3) carbides. In addition, the increased chromium concentration of filler materials leads to an increase in the volume fraction of the primary carbides in the matrix of hardfacing deposits. The buttering layer caused the formation of diluted hardfacing deposits. Also, it significantly reduced the hardness and wear rate of hardfacing deposits. Fe14-Fe14 hardfacing deposit has exhibited the best wear properties with a low coefficient of friction.

The Use of Raman Spectroscopy to Monitor Changes in the Intensity of Ratio of Integral Unsaturated Bands in Bio-Greases

Bio-greases were developed on the basis of vegetable oil obtained from Crambe Abyssinic seeds. An important aspect of this research is to monitor changes in their quality taking place under the influence of external factors. Raman spectroscopy was used to identify changes taking place in the bio-lubricant under the influence of mechanical and thermal forces. The performed tests reflected the operating temperature and friction load that may occur during actual operating conditions for the lubricated friction systems. The Raman spectra provided information on qualitative changes in the structure of the tested bio-lubricants at the molecular level. The integral intensity of the bands used to assess the degree of lipid unsaturation was adopted as the evaluation criterion. The influence of the oxidation process under the PetroOxy and wear test conditions on changes in the structure of the bio-lubricants was assessed. Variation in the integral intensity of the bands (I1655/I1440) proves that the structure of vegetable lubricants changes under the influence of the tests performed. Thermal and mechanical forces influence, the bands originating in unsaturated and result in a decrease in the oxidation resistance of vegetable lubricants.

Wear prediction of 3D-printed acrylonitrile butadiene styrene-carbon nanotube nanocomposites at elevated temperatures

Abstract In this study, multi-wall carbon nanotube (MWCNT) reinforced acrylonitrile butadiene styrene (ABS) nanocomposite filaments are produced. Filaments are examined through thermogravimetric analysis (TGA) and definitive scanning calorimetry (DSC) analysis. Produced nanocomposite filaments are used in the fused deposition modeling (FDM) process to manufacture parts. Wear tests are conducted on 3D-printed parts using wear test apparatus with an attached heating module under different ambient temperatures. Hence, the influence of CNT reinforcement, along with different FDM process parameters and varying test conditions on the wear behavior of 3D-printed ABS-CNT parts, are examined. Worn surfaces of the specimens are examined by scanning electron microscopy (SEM). Nonlinear autoregressive exogenous (NARX) models are proposed for the prediction of the wear behavior of 3D-printed ABS-CNT nanocomposites. While wear rate is taken as output, ambient temperature and amount of nanofiller are accounted as input parameters along with the variation of coefficient of friction (COF) which is obtained from measured frictional force and three input-one output model structure is proposed for NARX. The use of multiple input-single output (MISO) model structure and examining the wear behavior of 3D-printed ABS-CNT samples under different wear test conditions with different FDM process parameters are the novelties in this work.

Study of wear of contact surfaces of powder coatings and steel counterbodies under sliding friction at low climatic temperatures

The article presents the results of measuring the thermophysical data of friction units "wear-resistant coating — steel counterbody" under conditions of low climatic temperatures. The temperatures of friction pairs at various stages of wear during friction in cold and room conditions are determined. The mechanisms of wear of friction surfaces under various wear test conditions are established.

Microstructure and Wear Characterization of the Fe-Mo-B-C-Based Hardfacing Alloys Deposited by Flux-Cored Arc Welding.

An analysis of common reinforcement methods of machine parts and theoretical bases for the selection of their chemical composition were carried out. Prospects for using flux-cored arc welding (FCAW) to restore and increase the wear resistance of machine parts in industries such as metallurgy, agricultural, wood processing, and oil industry were presented. It is noted that conventional series electrodes made of tungsten carbide are expensive, which limits their widespread use in some industries. The scope of this work includes the development of the chemical composition of tungsten-free hardfacing alloys based on the Fe-Mo-B-C system and hardfacing technology and the investigation of the microstructure and the mechanical properties of the developed hardfacing alloys. The composition of the hardfacing alloys was developed by extending the Fe-Mo-B-C system with Ti and Mn. The determination of wear resistance under abrasion and impact-abrasion wear test conditions and the hardness measurement by means of indentation and SEM analysis of the microstructures was completed. The results obtained show that the use of pure metal powders as starting components for electrodes based on the Fe-Mo-B-C system leads to the formation of a wear-resistant phase Fe(Mo,B)2 during FCAW. The addition of Ti and Mn results in a significant increase in abrasion and impact-abrasion wear resistance by 1.2 and 1.3 times, respectively.

Identification of self-lubricative mode for the ultrasonic treated AA6061-B4C-CNT hybrid composites

This research investigates the self-lubricative behavior of boron carbide (B4C) and carbon nanotube (CNT) reinforced 6061 aluminium alloy hybrid composites. Hybrid composites were prepared by varying the volume percentages (5–15%) of B4C and CNT. Novel ultrasonic vibration (frequency of 20 kHz and power of 2.5 kW) assisted stir casting process was used for fabricating hybrid composites. A pin-on-disc type tribometer mounted with EN-8 as the counterface material was used to evaluate the friction and wear behavior of hybrid composites under dry sliding conditions. Normal loads ranging from 15–45 N and sliding speeds ranging from 1–2 m/s were applied during the experiments. The self-lubricative properties of different hybrid composites were assessed through the examination of the worn surface of pins using surface characterization techniques such as Scanning electron microscopy, Electron dispersive spectroscopy and Raman spectroscopy. The experimental results indicated that the addition of CNT particles increased the hardness of hybrid composites. The matrix strengthening efficiency of CNT was found to be greater at 10 vol.% of B4C, indicating a maximum hardness ranging from 102 to 109 VHN. In comparison, 10 vol.% of CNT hybrid composites showed superior tribological performance at all wear testing conditions. The mode of wear of hybrid composites suggested by the analysis on the worn pin surface was as follows: Scarce (5 vol.% CNT), Tribolayer (10 vol.% CNT) and Fracture (15 vol.% CNT).

Sliding wear behavior of a sustainable Fe-based coating and its damage mechanisms

The current industry demand is to identify suitable alternatives to the risk-of-supply prone and/or toxic, WC-Co and electrolytic hard chrome coatings without comprising the desired wear performance. Therefore, compositions based on abundantly available elements (e.g. ‘Fe’) that possess adequate wear resistance are desirable from health, sustainability and economic standpoints. In this work, crystalline Fe-based (Rockit-401) coatings were processed using two different thermal spray routes, i.e. HVOF and HVAF spraying. The influence of deposition route and processing conditions on the microstructure, porosity content, hardness and phase composition was examined. The as-deposited coatings were subjected to mild (5 N) and harsh (15 N) dry sliding wear test conditions by employing alumina ball as the counter surface material, and their wear performance was examined. Mild sliding wear test conditions (5 N) resulted in anomalous wear behavior, where the abrupt drop in CoF at several instances during the test was observed in all the investigated coatings. On the other hand, under harsh wear test conditions (15 N), such an abrupt dip in CoF was not observed. Detailed wear mechanisms of the coatings were revealed under different test conditions (5 N and 15 N). This work sheds light on processing, wear behavior and wear mechanisms of a sustainable and high-performance coating that fulfills non-toxic and sustainability goals in tandem for tribological applications.

Effect of Heat Treatment and Applied Load on Mechanical and Tribological Properties of Ni-B-CeO2 Composite Electroless Coating

Cerium oxide (CeO2) particle reinforced Ni-B composite coating was produced by electroless coating method from a Ni-B coating bath containing CeO2 particles. In the electroless plating bath, nickel sulfate hexahydrate ((NiSO4.6H2O) was used as nickel source, dimethylamine borane ((CH3)2NHBH3) as reducing agent, thiourea (CH4N2S) as stabilizer and sodium acetate (CH3COONa) as complexing agent. The aim of the study is to investigate the structural characterization of CeO2 particle reinforced coating and the effects of wear test conditions on its tribological properties. The surface morphology of the coating was performed by scanning electron microscope (SEM), and phase structure analysis was performed by X-ray diffraction (XRD). Nanohardness measurements were carried out with a nanoindenter device, and wear tests were done with a ball-on-disk test device. Worn surface analyzes were made using a 3D profilometer. Experimental results showed that the hardness of the coating increased with heat treatment; however, its tribological behavior changed depending on different loads

Wear resistance of laser cladding Fe50Cr40Si10 coating on AISI 1045 steel in elevated temperature

To improve the high-temperature wear resistance of a substrate, in this study, Fe50Cr40Si10 coating was prepared on AISI 1045 steel by the laser cladding technique and the microstructure was characterized by using an optical microscope (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that the coating with a fine and uniform microstructure has a good metallurgical bond with the AISI 1045 steel substrate. The upper layer of the coating is composed of typical equiaxed grains, and the bottom layer has columnar grains. The XRD pattern shows that the phase compositions are Fe-based solid solution (α phase) with Cr and Si and Fe-Cr intermetallics (α′ phase). The average microhardness of the coating is approximately 530 ± 37.5 HV0.5. The elevated-temperature dry sliding wear resistance of laser cladding Fe50Cr40Si10 coating was carried out on a pin-on-disk mode machine at different temperatures and loads. Under the same wear test conditions, the elevated-temperature wear rates of Fe50Cr40Si10 coating were much lower than those of AISI 1045 steel. When the load was 30 N, it was found that the wear mechanism of Fe50Cr40Si10 coating changed from abrasive wear and adhesive wear to oxidation wear with the increase in temperature. At the wear test temperature of 300 °C, the wear mechanism of the coating changed from oxidation wear to abrasive wear and adhesive wear with the increase in loads.

Wear Analysis of an Advanced Al–Al2O3 Composite Infiltrated with a Tin-Based Alloy

In this study, a hybrid material is produced, and the effect of different loads varying from 40 to 60 N against an EN-31 steel counter disk on its wear behavior under dry sliding conditions at room temperature is studied. The tribological behavior is studied via the pin-on-disk method and analyzed using primary wear parameters, such as the coefficient of friction (COF), mass wear, and specific wear rate. The obtained results are compared with the results for B83 babbitt under the same wear test conditions. Microstructural observation with scanning electron microscopy (SEM) is performed along with X-ray energy dispersive spectroscopy (EDX) for chemical analysis conduction. The results from the wear experiments indicate that the hybrid material possesses a lower COF, mass wear, and specific wear rate as well as a higher wear resistance in comparison to the B83 babbitt specimen when subjected to the same test conditions. The results from the wear experiments indicate that by applying different loads of 40, 50, and 60 N, the hybrid material possesses a lower mass wear, specific wear rate, and COF specifically at a load of 40 N in comparison to the B83 babbitt specimen under the same test conditions. It was also observed that by increasing the load under dry sliding friction, the hybrid material increases its mass wear and specific wear rate.

Investigating load-dependent wear behavior and degradation mechanisms in Cr3C2–NiCr coatings deposited by HVAF and HVOF

Wear resistant coatings that comply with non-toxic environment goals are highly desirable. Cr3C2–NiCr is a promising alternative to the toxic, ‘Co’- containing WC–Co coatings to mitigate wear. The purpose of this study was to examine the suitability of Cr3C2–NiCr coatings for automotive brake disc application by systematically investigating their dry sliding wear behavior at different test conditions. Therefore, High Velocity Air Fuel (HVAF) and High Velocity Oxy Fuel (HVOF) were employed to deposit Cr3C2–NiCr coatings. The powder feedstock and as-deposited Cr3C2–NiCr coatings were characterized for their microstructure and phase composition using SEM and XRD. Mechanical properties (hardness, fracture toughness), porosity and surface topography of the as-deposited coatings were evaluated. The coatings were subjected to sliding wear tests at different normal loads (5 N, 10 N and 15 N) using alumina ball as the counter surface. Coefficient of friction (CoF) evolution of HVAF and HVOF deposited coatings, along with their wear performance, was obtained for different normal load conditions. The wear performance ranking of HVAF and HVOF processed coatings was influenced by the test conditions, with HVAF coatings demonstrating better wear resistance than HVOF coatings at harsh test conditions and the HVOF coatings performing better under mild wear test conditions. Detailed post-wear analysis of worn coatings, the alumina ball counter-body and the resulting debris was performed to reveal the degradation mechanisms at different test conditions. Findings from this work provide new insights into the desirable microstructural features to mitigate wear, which can be further exploited to deposit wear-resistant coatings.

Evaluation of the residual stress of HVOF sprayed carbon coating after wear testing conditions using ANN coupled Taguchi approach

The as deposited carbon coating was successfully synthesized from agricultural waste using High Velocity Oxy-fuel (HVOF) thermal spray deposition technique. The surface topography of as deposited carbon coating, confirms the presence of molten, semi-molten, and un-melted grains along with the formation of lamellae. Taguchi L9 orthogonal Array (OA) and Artificial Neural network (ANN) models were used to predict and optimize the process parameters for residual stress after wear testing conditions. The estimated mean (μ) obtained from optimal responses is 11 MPa. Three confirmation tests of as-deposited carbon coating for residual stress after wear testing conditions were conducted for optimal level of parameters at level 3 of Temperature (250 °C), level 3 of sliding velocity (0.3 m s−1), and level 3 of load (80 N). The percentage (%age) contribution of as-deposited carbon coating for residual stress after wear testing conditions from Analysis of Variance (ANOVA) prediction was highest for temperature (51.23%), followed by 32.8% of sliding velocity, and 12.5% for a load.

Tribological behaviour of AZ91D/ultra-high-temperature ceramic composites at room and elevated temperatures

In this research work, the tribological behaviour of an AZ91D alloy and its composites reinforced with different titanium-based ultra-high-temperature ceramic particulates was investigated. Titanium-based ultra-high-temperature ceramic materials (5 wt%) such as titanium carbide, titanium boride and titanium nitride was used for the fabrication of three different composites, namely ATC, ATB and ATN, respectively. The proposed composites were prepared using a novel ultrasonic treatment-assisted stir-squeeze casting technique. Material characterization was performed using scanning electron microscopy and X-ray diffraction techniques. The porosity and hardness of the composites were determined prior to the wear test. In the pin-on-disc tribometer, the wear test was carried out at room temperature by varying the normal load (12.5–50 N) and the sliding speed (0.25–1 m/s). In addition, at a temperature of up to 200 °C, the tribological behaviour of the composites was assessed. The homogeneous distribution of ultra-high-temperature ceramic particles in the matrix was confirmed by the analysis of the microstructure using scanning electron microscopy images. The X-ray diffraction results showed that the reinforcement materials in the matrix were thermally stable. The hardness of the ATC, ATB and ATN was improved by approximately 31%, 33.8% and 29.6%, respectively. In comparison, at all wear testing conditions, ATB demonstrated superior tribological performance, while the performance of ATN was poor and ATC was moderate. Abrasion, oxidation and delamination were the wear mechanisms at room temperature. At elevated temperatures, oxidation, delamination, thermal softening and plastic deformation wear mechanisms were significant..

Microstructure and performance of magnetic field assisted, pulse-electrodeposited Ni–TiN thin coatings with various TiN grain sizes

In this manuscript, Ni–TiN thin coatings were deposited on 45 steel substrate surfaces using a magnetically assisted pulse electrodeposition (MAPE) technique. The surface topographies, chemical compositions, microstructures, microhardnesses, and corrosion properties of the Ni–TiN thin coatings were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), scanning probe microscopy (SPM), triboindenter in-situ nanomechanical testing, as well as corrosion and wear testing. Results indicated that the Ni grain size in the Ni–TiN thin coatings gradually decreased as the grain size of TiN decreased from 180 nm to 32 nm. The mean sizes of TiN nanoparticles and Ni grains in the NT32 thin coating were 41.5 nm and 379.2 nm, respectively. The microhardness of NT180 was the lowest among all three coatings with a mean value of 597.2 HV. Conversely, the mean microhardness of the NT32 thin coating was the highest at 902.9 HV. The size of the TiN particles had a significant effect on the corrosion properties of the Ni–TiN thin coatings, and the corrosion curve of the thin coating of NT32 slowly grew throughout the experiment. Under the same wear test conditions, the NT180 coating showed higher wear mass loss, while the wear mass loss of the NT32 thin coating was the lowest at 36.4 mg.