Nickel-chromium Alloy Research Articles

Residual stress effects during additive manufacturing of reinforced thin nickel–chromium plates

Additive manufacturing (AM) is a powerful technique for producing metallic components with complex geometry relatively quickly, cheaply and directly from digital representations; however, residual stresses induced during manufacturing can result in distortions of components and reductions in mechanical performance, especially in parts that lack rotational symmetry and, or have cross sections with large aspect ratios. Geometrically reinforced thin plates have been built in nickel–chromium alloy using laser-powder bed fusion (L-PBF) and their shapes measured using stereoscopic digital image correlation before and after release from the base-plate of the AM machine. The results show that residual stresses cause potentially severe out-of-plane deformation that can be alleviated using either an enveloping support structure, which increased the build time substantially, was difficult to remove and wasted material, or using buttress supports to the reinforced edges of the thin plate. The buttresses were quick to build and remove, minimised waste but needed careful design. Plates built in a landscape orientation required out-of-plane buttresses while those built in a portrait orientation required both in-plane and out-of-plane buttresses. In both cases, out-of-plane deformation increased on release from the baseplate but this was mitigated by incremental release which resulted in out-of-plane deformations of less than 5% of the in-plane dimensions.

Comparison of the accuracy of impressions made of 2 implants with interfering axial convergence with CAD-CAM impression copings and the altered cast technique: An in vitro study

Statement of problemStudies that evaluated the accuracy of different methods for making an impression of 2 implants in close proximity or with adverse axial convergence are lacking. PurposeThe purpose of this in vitro study was to compare the accuracy of impressions made with metal and resin computer-aided design and computer-aided manufacturing (CAD-CAM) impression copings and an altered cast technique. Material and methodsTwo implant analogs with an interimplant angulation of 50 degrees were placed in an acrylic resin master model. Thirty impressions were made with 3 techniques (n=10). Two angled abutments were scanned to print 40 impression copings from a castable resin, half of which were cast with nickel-chromium alloy (M-CAD) and half of these were used in the R-CAD group. Impressions were made and poured. For the altered cast technique (Alt-cast), casts with only the mesial analogs were made and hollowed at the site of the distal analogs. The position of the distal analogs was transferred by resin indices (n=10) fabricated with light-polymerized resin on the master model. The linear displacements of mesial (ΔR1) and distal (ΔR2) analogs and the interanalog distance (ΔRt) were measured with a coordinate measuring machine. The data were analyzed by using the Kruskal-Wallis and Dunn post hoc tests (α=.05). ResultsNo significant difference was found between the M-CAD and R-CAD groups regarding ΔR1 (P=.722), ΔR2 (P=.576), or ΔRt (P=.939). However, the Alt-cast group differed from the M-CAD group in ΔR1 (P<.001), ΔR2 (P<.001), and ΔRt (P=.002) and also from the R-CAD group in ΔR1 (P=.001), ΔR2 (P=.002), and ΔRt (P=.003). ConclusionsThe impressions made with metal and resin CAD-CAM impression copings were more accurate than those made with the Alt-cast technique although all techniques had acceptable accuracy.

Investigation of changes in the structure of heat-resistant iron-containing chromium-nickel alloy as a result of long-term operation

Pyrolysis furnaces operate in harsh temperature and power conditions. Radiant coils are the most vulnerable part in their design. The coil pipe operates in two modes: operational - at a constant pressure and temperature not exceeding 1050 &deg;С, and cleaning mode, which is characterized by increased pressure and higher temperature (about 1100 &deg;С) compared to the operating one, which leadsto a thermal force effect. Such operating conditions of coil pipes lead to changes in the structure and properties of the material. In this regard, chromium-nickel steels are widely used for the manufacture of coils, and for operation at higher temperatures (1000-1050 &deg;C), the content of chromium and nickel is increased, obtaining iron-containing chromium-nickel alloys, to ensure a stable austenitic structure. Identification of the dominant damaging mechanism makes it possible to determine the remaining resource and replace the coils in time to prevent possible emergencies. It is obvious that structural changes in the pipe metal will have a decisive influence on the performance of the structure as a whole. This paper presents the results of a study of the influence of some operational factors on the state of the metal of pipes of a standard furnace coil made of heat-resistant iron-containing chromium-nickel alloy. A change in the matrix microstructure in the form of partial homogenization of austenite was revealed. The fact of the occurrence of carbide reactions has been established. The presence of an oxidation zone mainly along the boundaries of dendrites was revealed, and the main types of oxides were determined. The dominant damaging mechanism of radiant tubes during operation has been determined.

Kinetics and Mechanical Characterization of Hard Layers Obtained by Boron Diffusion in 80/20 Nickel–Chromium Alloy

This study examines the formation of hard layers containing Ni-B and Cr-B on the surface of 80/20 nickel–chromium alloy. The work evaluates the mechanical properties of the boride layers using instrumented nanoindentation. In addition, the growth kinetics of the coatings were assessed by applying a kinetic model that relates the layer thickness with the experimental parameters of temperature and treatment time. First, the boride layers were achieved using the powder-pack boriding process in a conventional furnace. The treatment time was set at 2, 4, and 6 h at temperatures of 900, 950, and 975 °C, respectively. The microstructure of the layers was analyzed by X-ray diffraction. The thickness of the layers showed a closed correlation with the experimental parameters of time and temperature, and was established between 38.97 and 156.49 µm for 2 h to 900 °C and for 6 h to 975 °C, respectively. The hardness and Young’s modulus values agree with those presented in the literature for boriding nickel alloys, being in the range of 1.3 GPa on average and 240 to 270 GPa, respectively. The resulting layers exhibited a characteristic diffusion zone where the hardness values decrease gradually without the typical high hardness gradient observed on borided steels.

Investigation of the deformation behavior and mechanical characteristics of polycrystalline chromium-nickel alloys using molecular dynamics.

In this study, the mechanical properties and plastic deformation responses of nanocrystalline Cr-Ni alloy were investigated via tensile tests by molecular dynamics (MD) simulation. The effect of various compositions, various grain sizes (GSs) from 4.7 to 11.0nm, and various temperatures from 300 to 1500K is analyzed. The results indicate that the yield strength of the polycrystalline Cr-Ni alloy decreases as decreasing GS, which shows the inverse Hall-Petch relation in the metal softening as reducing GS. Young's modulus (E) increases in the order of the increasing GSs and single crystalline. E rises as raising the percent of Ni from 5 to 15% and then decreases as increasing %Ni to 20%. Besides, E is the linear decrease function with increasing temperature. The maximum stress decreases as increasing temperature and increasing %Ni from 5 to 15%. But that decreases as increasing %Ni from 15 to 20%. The maximum stress value of single crystalline is smaller than that of polycrystalline. The high shear strain zones depend on the GS and alloy composition. The shear strain zones focus on the grain boundary at a low temperature and disperse over the entire specimen when the specimen works at a high temperature. The reason is that the grain boundary helps release stresses to prolong the plastic deformation period to prevent rapid specimen destruction.

The Influence of Metal Coping Design on Fracture Resistance of Porcelain-Fused-to-Metal Crown

The porcelain-fused-to-metal crown is the most popular indirect restoration in dentistry due to its high fracture resistance and low cost. However, unaesthetic labial margin is unacceptable to patients. Metal collar causes dark discoloration, which is worsened by gingival recession. Modification in metal collar coping has been developed to combine high fracture resistance of metal and high aesthetic of porcelain. Modification in crown fabrication including structure and composition of both nickel chromium alloy and feldspathic porcelain; application of self-cured resin cement and digital method; is meant to improve aesthetics without compromising fracture resistance. This study was an experimental laboratory research to evaluate fracture resistance of porcelain-fused-to-metal crowns with different metal coping designs. A total of 20 samples were used and divided into 4 groups according to different coping designs: (1). full metal collar; (2). full metal collarless; (3). modified metal collarless with 1.5 mm reduction; (4). modified metal collarless with 2 mm reduction. Universal Testing Machine (LRXPlus, Lloyd) was used to measure fracture resistance of all crowns. Average fracture resistance value for group 1 was 988.42 N; Group 2 was 1180.15 N; Group 3 was 1089.47 N; Group 4 was 1202.61 N. The results of statistical analysis showed that there was a difference in fracture resistance among porcelain-fused-to-metal crowns with different coping designs, although the value was not statistically significant. The higher coping reduction at labial margin, the higher the fracture resistance and standard deviation.

An In Vitro Assessment of Marginal Accuracies in Copings Fabricated With Two Dissimilar Alloys: An Original Research Study.

Background: Marginal accuracy is one of the serious factors that play a key role in the overall success of prostheses. It is openly associated with marginal activities of microorganisms, which may develop micro-leakage and other problems. Therefore, this in vitro study was conducted to assess marginal accuracies in copings fabricated with two different alloys used in fixed partial dentures.Materials and Methods: Two popularly used metal alloys, Mealloy (nickel-chromium alloy) (Dentsply India Pvt. Ltd., New Delhi, India) and Supranium (nickel-chromium alloy) (Bombay Precision Alloy Inc., Mumbai, India), were studied. Group 1 has 20 copings of Mealloy; group 2 also has 20 copings of Supranium. Blue inlay wax was used for wax pattern fabrication. All copings were cast and made by similar casting techniques. After adequate seating of copings on metal dies, the marginal difference was assessed under a stereomicroscope at typical intensification. All measurements were noticed and converted to the nearest micron. For each coping sample, four measurements were recorded; however, the means of all four surfaces were taken into account for further analysis.Results: All interrelated data was processed by statistical analysis using the Statistical Package for the Social Sciences (SPSS) software version 22.0 (IBM Corp., Armonk, NY, USA). The overall mean marginal gap of the samples of group 1 was higher than group 2. For group 1 coping samples, a maximum mean marginal gap of 43.379 was noticed at the buccal surface of the copings. P-value computation revealed non-significant values (0.60). For group 2 coping samples, a maximum mean marginal gap of 41.218 was found at the buccal surface of the copings. The measured value was 41.218. One-way ANOVA analysis showed that the degree of freedom was 132.13 for cumulative comparison, while it was 2.930 and 6.837 for calculations between groups and within groups, respectively. Two-sample t-test assessments revealed a p-value of 0.001 (significant) for group 1 and a p-value of 0.810 (non-significant) for group 2.Conclusion: The marginal space at the margin of the metal coping and the die was minimum for Supranium and maximum for Mealloy. Also, highly significant values were also identified for the metal samples of Supranium. Additionally, the selection of the perfect metal alloy should be entirely dependent on operator skills and clinical decision-making.

Study of the Corrosion of Nickel-Chromium Alloy in an Acidic Solution Protected by Nickel Nanoparticles.

This study uses nickel nanoparticles coated on the nickel–chromium (Ni–Cr) alloy by the electrodeposition technique to protect the alloy against corrosion. An open-circuit potential and potentiodynamic and linear polarization resistance in a 1 M H2SO4 solution saturated with carbon dioxide were used to study the anticorrosion performance of nanoparticle coatings. When coated with nanomaterials, the corrosion rate of Ni–Cr alloy was lower than when it was bare, and the potential for corrosion increased from −0.433 V for uncoated Ni–Cr alloy to −0.103 V when the electrodes were exposed to saturated calomel. Electrochemical experiments show that nickel-coated Ni–Cr alloy corrosion in sulfuric acid media has high protective characteristics, with an efficiency of 83.69% at 0.165 mA/cm2 current density when pH = 1 is used. As demonstrated by the results of this research, the nickel–chromium alloy can be protected from corrosion in acidic media by a low-acidity bath coating layer. Surface morphologies have shown that coatings at different acidic scales may be able to resist an acid attack because of their excellent adherence to the nickel–chromium alloy surface. Measures for determining and studying the composition of the alloy surface’s protective covering were improved using X-ray diffraction (XRD).

Electrogalvanism in Oral Implantology: A Systematic Review.

Purpose The objective of this work is to study galvanic corrosion of different couples of prosthetic and implant alloys through the realization of a systematic review. Materials and Methods An electronic search was performed on Pubmed, Google Scholar, Scopus, ScienceDirect, EbscoHost, and Web of Science for published studies related to electrogalvanism in oral implantology. The keywords used were “dental implants” and “galvanic corrosion.” Two independent readers read the scientific articles. Results From 65 articles initially identified, only 19 articles met the eligibility criteria. The evaluation of the selected articles allowed us to determine the parameters compared, such as the resistance to galvanic corrosion, the influence of fluorine and pH on the electrochemical behavior, and the release of metal ions and their cytotoxicity. Indeed, Ti6Al4V and precious alloys coupled to titanium were found to be the most resistant to galvanic corrosion, followed by cobalt-chromium alloys and nickel-chromium alloys which were least resistant. This resistance decreases with increasing fluorine concentration and with decreasing pH of the environment. Discussion. The implant-prosthetic system's galvanic resistance is influenced by many intrinsic factors: alloy composition and surface condition, as well as extrinsic factors such as pH variations and amount of fluorine. The effects of oral electrogalvanism are essentially the result of two main criteria: effects due to electric currents generated by corrosion and effects due to the release of metal ions by corrosion. Conclusion To avoid this phenomenon, it is wise to follow the proposed recommendations such as the use of the minimum of distinct metals as much as possible, favoring the commercially pure titanium implant of Ti6Al4V, opting for the choice of couples, titanium/titanium, favoring daily mouthwashes of 227 ppm of fluoride, and avoiding fluorinated acid solutions.

Effect of the Passive Oxide Films Structure and Surface Temperature on the Rate of Anodic Dissolution of Chromium-Nickel and Titanium Alloys in Electrolytes for Their Electrochemical Machining. Part 2. Anodic Dissolution of Titanium Alloys in Nitrate and Chloride Solutions

An experimental study of the anodic dissolution of titanium and its alloys, including pulsed dissolution (up to 100 A/cm2) under control of hydrodynamic conditions and surface temperature in nitrate and chloride solutions, showed that the process is carried out through the electrochemical formation of anodic oxide films (AOF) which can be chemically dissolved. An AOF has a bilayered structure, i.e. two barrier films on the interface with a metal and a solution. Its model is PDM-III (Point Defect Model). At certain conditions, it is possible to achieve a steady state in which the film growth rate is compensated by the rate of its chemical dissolution (observed at pulsed conditions). In this case, over 100% current efficiency based on the ionization of titanium in the oxidation state is achieved. During the conducted experiments, when treated with the direct current, the rate of the electrochemical formation of an AOF exceeded the rate of its chemical dissolution, which led to a decrease in to current efficiency which did not exceed 75%. An increase of the dissolution rate takes place with an increase in the electrolyte flow rate. Upon reaching the thermokinetic instability (TKI) of the AOF (thermal explosion due to a feedback rate of the electrochemical reaction-surface tem-perature-rate of an electrochemical reaction), the interaction of electrolyte components with the surface free of the film takes place, and, as a result, an “anomalous” anodic dissolution is observed with the current efficiency greater than 100%. Regardless the nature of the electrolyte, TKI is achieved at a current density of 1 A/cm2. It is shown that in nitrate solutions with certain parameters of pulsed processing (duty factor 2, dc 50%), the dissolution rate, and, in the case of electrochemical machining, the feed rate of a cathode-tool, can be more than twice higher than the rate of machining with the direct current of the same density.

Application of Pedagogical Technologies on the Topic: "Polymer Composite Materials and their Significance"

Composite materials are soluble and insoluble, and its effectiveness is enhanced by the addition of additives. Natural and artificial composite materials, with a natural group of cellulose fibers in the body and stem of the plant, containing lignin, and for bones in the human and animal organism, the binding of thin, mature phosphate salts to plastic collagen is characteristic. Powder composite material (PCM) is characterized by resistance to deformation, cutting, welding, corrosion and heat .In the manufacture of disks and shovels, the properties of nickel-chromium alloys and powders with the addition of hafnium oxide are additionally improved.

Investigation of the Nature of the Interaction of Me-MeN-(Me,Mo,Al)N Coatings (Where Me = Zr, Ti, or Cr) with a Contact Medium Based on the Ni-Cr System

This paper discusses the results of a study focused on the nature of the interaction of Me-MeN-(Me,Mo,Al)N coatings (where Me = zirconium (Zr), titanium (Ti), or chromium (Cr)) with a contact medium based on the Ni-Cr system. The studies were carried out during the turning of nickel–chromium alloy at different cutting speeds. The hardness of the coatings was found, and their nanostructure and phase composition were studied. The experiments were conducted using transmission electron microscopy (TEM), X-ray diffraction (XRD), and selected area electron diffraction (SAED). According to the studies, at elevated cutting speeds, the highest wear resistance is demonstrated by the tools with the ZrN-based coating, while at lower cutting speeds, the tools with the TiN- and CrN-based coatings had higher wear resistance. At elevated cutting speeds, the experiments detected the active formation of oxides in the ZrN-based coating and less active formation of oxides in the CrN-based coating. No formation of oxides was detected in the TiN-based coating. The patterns of cracking in the coatings were also studied.

Effect of the Passive Oxide Films Structure and Surface Temperature on the Rate of Anodic Dissolution of Chromium-Nickel and Titanium Alloys in Electrolytes for Their Electrochemical Machining. Part I. Anodic Dissolution of Chromium-Nickel Steel in a Nitrate Solution

Experimental study of the chromium-nickel steel Cr18Ni10 anodic dissolution in a nitrate solution with electrical conductivity 0.15 S/cm in a pulse – galvanostatic mode at pulse durations 20–100 µs and current densities 0.01–100 A/cm2, with a change in the duty cycle 10–100% (direct current) at various hydrodynamic conditions and control the surface temperature, that the results obtained are consistent with the hypothesis that the process proceeds through the formation of oxide films of a semiconductor nature with a different type of conductivity (a film containing point defects, Point Defect Model, PDM). Under sta-tionary conditions of the existence of PDM-II, the rate of its electrochemical formation is compensates by the rate of its chemical limiting value of the weight loss per unit of a passed charge (0.16–0.18 mg/C) (takes place under pulse conditions), which corresponds to a cur-rent efficiency close to 100% based on the highest degree of oxidation of the steel compo-nents. When transition to direct current takes place, thermokinetic instability of the film is observed (its formation and destruction due to thermal explosion). Under these conditions, the current efficiency can not only reach 100% based on the lowest degree of oxi-dation of the steel components (thermal activation) but also exceed this value due to the chemical interaction of the electrolyte with the film-free surface.

An In Vitro Study on the Shear Bond Strength of Feldspathic Porcelain to Nickel Chromium Alloy and Cobalt Chromium Alloy after Various Surface Treatments.

Background To evaluate and compare the shear bond strength of feldspathic porcelain to four distinctively surface-treated Ni-Cr and Co-Cr alloys and to assess the impact of oxidation-heat treatment on porcelain to base metal alloy bond strength. Methods 40 specimens each of nickel-chromium alloy and cobalt-chromium alloy were cast. A total of four groups of specimens were created. Group I was surface-treated by sandblasting with 50 μm alumina particles, Group II was surface-treated by sandblasting with 110 μm alumina particles, Group III and Group IV were surface-treated with 250 μm alumina particles. In Group IV, after sandblasting initially with 250 μm alumina particles, the alloys were subjected to oxidation and resandblasting with 250 μm alumina particles. Each of the specimen was coated with opaque and body porcelain and fired to a total thickness of 2 mm porcelain. A universal measuring machine was used to assess shear bond strength at a crosshead speed of 0.5 mm/min. Results Two-way ANOVA followed by Tukey's post hoc test was used to assess the significant difference within the groups. Unpaired t-test was used for the intergroup comparison of the obtained data. The study showed that the size of the air abrasion particles used for sandblasting significantly influenced the porcelain to metal surface bond strength, with p value <0.001. The bond strength values of the two alloys tested showed no major variations. Result also showed that oxidation influences the metal-ceramic bond strength. Conclusions The bond strength of the metal-ceramic interface is influenced by the alloy's surface treatment. The oxidation process impacts the bond strength of the metal-ceramic system.

Surface Characteristics and Adhesion of Veneering Composite Resin to PAEK-Based Substructure Restorative Materials.

To evaluate and compare the shear bond strength (SBS) of composite veneering material to polyetherketoneketone (PEKK), polyetheretherketone (PEEK), zirconia (YZ), and nickel-chromium alloy (NiCr) substructure restorative materials. Forty samples (12 × 2 mm) were prepared from four materials: PEKK, PEEK, zirconia, and NiCr alloy (n = 10). The Vickers hardness was evaluated before preparing the surface for bonding by shot-blasting using 110 μm Al2 O3 particles. The surface roughness (Ra) of each sample was determined using a noncontact optical profilometer. The veneering resin was bonded onto each sample following primer application. The prepared samples were then subjected to an SBS test using a universal testing machine at 0.5 mm/min crosshead speed. Failure modes and surface topography following debonding were assessed. The data were statistically analyzed using ANOVA and Tukey'spost-hoccomparison test (p < 0.05). RESULTS: The highest and lowest mean surface roughness was observed in PEEK (3.45 ±0.13 μm) and NiCr (1.87 ±0.07 μm) materials, respectively. A significant difference in roughness values was observed between the materials except for NiCr and YZ (p = 0.547). Concerning SBS, PEEK and NiCr exhibited the highest (16.23 ±0.96 MPa) and lowest (10.1 ±0.63 MPa) values. The mean difference in SBS indicated a statistically significant difference between the material groups (p < 0.01). PEKK materials demonstrated significantly lower SBS than PEEK and significantly higher SBS values than conventional zirconia and alloy materials. A positive and significant correlation between mean roughness and SBS was observed, but the causality could be either intrinsic to the material or the roughness.

Plasma-Beam Processing of Tools Made of SiAlON Dielectric Ceramics to Increase Wear Resistance When Cutting Nickel–Chromium Alloys

This research aimed at an increase in wear resistance of round cutting plates manufactured with SiAlON dielectric ceramics through deposition of wear-resistant coatings. To increase effectiveness of the coatings, their adhesion was improved by the removal of defective surface layers from the cutting plates before the deposition. As the depth of caverns and grooves appearing on the cutting plates due to manufacturing by diamond grinding reached 5 µm, a concentrated beam of fast argon atoms was used for the removal of defective layers with a thickness exceeding the depth of caverns and grooves. At the equal angles of incidence to the front and back surfaces of the cutting wedge amounting to 45 degrees, two-hour-long etching of rotating cutting plates provided removal of defective layers with thickness of ~10 µm from the surfaces. After the removal, the cutting edge radius of the plates diminished from 20 to 10 µm, which indicates the cutting plates’ sharpening. Wear-resistant TiAlN coatings deposited after the etching significantly improve the processing stability and increase wear resistance of the cutting plates by not less than 1.7 times.

Comparing Castability of Nickel-Chromium, Cobalt-Chromium, and Non-Precious Gold Color Alloys, Using two Different Casting Techniques.

Statement of the Problem: The castability of nonprecious gold color alloy using torch/ centrifugal and induction/vacuum-pressure casting techniques has not been studied yet.Purpose: This study was conducted to compare the castability of nickel chromium, cobalt-chromium and nonprecious gold color alloy using torch/centrifugal and induction/ vacuum-pressure casting techniques.Materials and Method: In this in vitro study, a total number of 54 identical acrylic wax meshes were prepared and divided into 6 different groups of 9 each. Group 1: nickel-chromium alloy, which was casted with induction technique. Group 2: nickel-chromium alloy was casted with centrifugal technique. Group 3: cobalt-chromium alloy was casted with induction technique. Group 4: cobalt-chromium alloy was casted with centrifugal technique. Group 5: nonprecious gold color alloy was casted with induction technique. Group 6: nonprecious gold color alloy was casted with centrifugal technique. Then castability of specimens was measured using modified Whitlock’s method. The results were analyzed using two way ANOVA and post hoc tests.Results: ANOVA test revealed no statistically significant difference between different alloys with a p Value of 0.313. Moreover, it represented no significant differences within the groups regarding alloy types and casting techniques with a p Value of 0.511 and 0.682, respectively.Conclusion: No significant difference was found in the castability value of nickel-chromium, cobalt-chromium, and nonprecious gold color alloys. In addition, the castability value of three alloys tested in this study was not different by using torch/centrifugal or induction/vacuum-pressure casting machines.

Fatigue Resistance of Cast-on Implant Abutment Fabricated with Three Different Alloys.

This study aimed to evaluate fatigue resistance of cast-on implant abutment using three alloys. Forty specimens of implant-supported crowns were prepared; Group 1 (TA) stock titanium abutments, Group 2 (GS) abutment cast with 40% gold alloy, Group 3 (GP) abutment cast with palladium alloy, and Group 4 (CN) abutment cast with nickel-chromium alloy. Specimens were cyclic loaded at 20 Hz, starting from 200 N (5,000 cycles), followed by stepwise loading of 400, 600, 800, 1,000, 1,200, 1,400, 1,600, and 1,800 N (30,000 cycles/step). Specimens were loaded until failure or reached 245,000 cycles. The withstand cycles were analyzed using one-way analysis of variance and Weibull survival analysis. Fracture surfaces were examined using scanning electron microscopy. The results of withstand cycles were TA (189,883 ± 22,734), GS (195,028 ± 22,371), GP (187,662 ± 22,555), and CN (200,350 ± 30,851). The statistical analysis showed no significant difference between the groups (p = 0.673). Although CN has higher Weibull characteristic strength which means greater durability, its lower Weibull modulus demonstrated less structural reliability. Consistent failures at implant fixture level were also found in CN group.

Friction and wear properties of short time heat-treated and laser surface re-melted NiCr-WC composite coatings at various dry sliding conditions

In the present study, the effect of various weight percentages (0, 20, 30, and 40 wt.%) of Tungsten Carbide (WC) reinforcement in the Nickel-Chromium (Ni-Cr) alloy was investigated. The coatings were deposited on a 316L stainless steel substrate using Plasma Transferred Arc Welding (PTAW) process. Additionally, the As Welded (AW) NiCr-WC coatings were subjected to Short Time Heat-Treatment (STHT) and Laser Re-Melting (LRM) processes and a comparative study has been carried out with that of AW coatings. X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Vickers hardness and Pin on disc wear testing facilities were employed to characterize the phase structures, microstructure, dilution, crystallization, hardness and wear properties of the deposits. Wear mechanisms were studied using the 3D surface analyzer and SEM images. The STHT and LRM coatings showed an increased hardness and more crystalline phases than the As-Welded (AW) coatings. The correlation between the intermetallic phases, residual stress, microstructural evolution and friction-wear behaviour among the AW, STHT and LRM NiCr and NiCr-WC coatings were discussed in detail.

High temperature (900 °C) sliding wear of CrNiAlCY coatings deposited by high velocity oxy fuel thermal spray

Nickel based superalloy are in demand for high temperature applications and their corrosion, erosion and wear resistance have been investigated for a long time. Nickel chromium (NiCr) alloys are widely used for corrosion resistant coatings, while chromium carbide nickel chromium (CrC-NiCr) alloys are preferred for wear resistant coatings at high temperature. In this study CrNiAlCY coatings were deposited via a liquid fuelled high velocity oxy fuel (HVOF) thermal spray using two spray parameters and tested as wear resistant coatings. Effects of processing parameters on microstructure and mechanical properties of the coatings were investigated. Results showed that higher oxygen flow rates are critical for obtaining coatings with lower porosity and higher microhardness. Coating with lower porosity and higher hardness was chosen for both room temperature (~24 °C) and high temperature (900 °C) unlubricated sliding wear tests in a ball on disc setup. The coating was tested against alumina counterbody under 3 different loading conditions (10, 30 and 60 N). The wear rate of the coating was directly proportional to the applied load at room temperature. In the room temperature tests, wear debris was produced, which then oxidised and pushed away to the edges of the wear track. On the other hand, wear debris was smeared on the wear surface at high temperature tests. The surface was oxidised into Cr 2 O 3 at high temperatures, which acted as a protective layer. Although thermal softening took place at higher temperatures, wear rates under 10 and 30 N were similar to room temperature values due to the protective oxide layer formed on the top surface; however, the oxide layer under 60 N could not withstand the load, started to crack and lost its protective ability. • CrNiAlCY coatings have been produced using a liquid-fuelled HVOF thermal spray. • Effects of spray parameters on the microstructure and hardness studied. • Wear performance was investigated against the alumina counter body. • 2 Different temperature settings were used during the wear tests.