Conventional Casting Research Articles

Investment casting of porous Mg-alloy networks biomechanically tuned for bone implant applications

AbstractManufacturing technology has been refined and described for the fabrication of honeycomb-based bioresorbable networks for temporal bone replacement applications. Two novel techniques, digital light processing and investment casting, were utilized to produce customized, shape-optimized cellular constructs with additional orifices promoting tissue ingrowth during osteo-regeneration. For this purpose, a conventional magnesium casting alloy (AZ91) was chosen. Numerical simulations were conducted to predict the compressive behavior of the proposed biodegradable lightweight scaffolds. Spatial castings were adjusted to possess mechanical properties comparable to the ones of cortical or trabecular bones. Two kinds of protective coatings (plasma electrolytic oxidation and organic ones based on natural polyphenols from tea extract) were deposited and characterized. They can be utilized to control the degradation rate during exploitation to achieve a predictable implant lifespan. The elaborated layers aim to mitigate the rapid corrosion of magnesium substrates by prolonging their bioresorption time and thus expanding their applicability in osseointegration. To evaluate this assumption, immersion tests in phosphate-buffered saline were performed, showing better chemical resistance of PEO coating and as-cast sample (for both mass gain by below 1%), and visible increase in mass of sample coated with organic coating (increase by almost 5%). Compressive strength results from numerical approach were further validated by experimental compression tests, showing that PEO coating deteriorated compressive strength by almost 3%, and organic coating improved it by over 9%. Results achieved in numerical approach were better than expected for stiffer sample, and slightly lower for the one with bigger pores.

Microstructure evolution of AlSi10Mg alloy in RAP process

Abstract With its computer-aided layer-by-layer production approach, additive manufacturing (AM) and powder bed laser fusion (PBLF) paved the way to produce metallic parts more precisely than any other manufacturing technique. However, the combinability and the interaction of this relatively new manufacturing technique with the other near-net shape production techniques is still a mystery. In this study, the recrystallization and partial melting (RAP) behavior, which is a feedstock production approach for semisolid forming methods, investigated on AlSi10Mg parts produced by PBLF and conventional casting were compared in terms of microstructural and hardness evaluations. After the reheating process, the globalization of Si particles and the breakdown of the Si network around the melt pools were displayed with light microscope and scanning electron microscope (SEM) images. The hardness values of the PBLF as-fabricated specimens were found to be significantly higher than the as-cast specimens; however, the values were almost equaled after the RAP treatment and even got lower on the bottom and top regions of the PBLF samples after 20 min of reheating because of the enlarged shrinkage porosities and the coarsened morphology.

Regulating microstructure and mechanical properties of the as-cast Mg-4Zn-0.5Y-0.5Nd alloy by heat treatment

The Mg-4Zn-0.5Y-0.5Nd alloy was designed and fabricated by conventional casting with subsequent heat treatment to regulate the microstructure and mechanical properties. The microstructure, secondary phase, mechanical properties, and fracture behavior were analyzed to elucidate the influencing mechanism. The results reveal that the as-cast alloy is composed of equiaxed grains with large sizes and discontinuously distributed secondary phases. Moreover, the secondary phase is mainly W-Mg3Zn3Y2, which partly forms the eutectic structure. The solid solution treatment coarsens the equiaxed grains and transforms the secondary phase into near continuous distribution. The Mg41Nd5 phase appears and volume fraction of secondary phase decreases a little. The combining of solid solution and aging treatment increases grain size and volume fraction of secondary phase more or less. Furthermore, the Mg24Y5 phase appears and secondary phases have been changed into semi-continuous distribution. After heat treatment, the average grain size reaches its maximum value of 107.18 μm, and the volume fraction of secondary phase climbs up to 2.73 %. Moreover, the solid solution treatment weakens the crystallographic orientation preference along {0001} but induces diversified crystallographic orientation preference. The heat treatment increases microhardness from 57.2 HV0.1 of the as-cast state to 70.5 HV0.1 of the heat-treated state. Comparatively, the solid solution treatment decreases mechanical properties, while the solid solution and aging treatment increase strength and ductility simultaneously. Especially for the ductility, it has been improved by more than 80 %, which is beneficial to the subsequent thermalmechanical processing greatly.

In-vitro study of Ti6Al4V alloy fabricated by laser-based additive manufacturing for orthopedic implant applications

The Ti6Al4V alloy is widely used in orthopedic implants due to its excellent mechanical properties and biocompatibility. However, traditional manufacturing techniques are unable to fabricate complex geometrical shapes with tailored properties. This leads to premature failure due to wear, corrosion, and poor osseointegration. Recent advancements in laser-based additive manufacturing, particularly in direct metal laser sintering (DMLS), offer new opportunities to produce Ti6Al4V implants with tailored microstructures, mechanical properties, and biocompatibility. However, wear, corrosion, and cell viability behavior, required for evaluating the biomedical applicability of Ti6Al4V alloy produced through the DMLS route have not been reported. The present study fulfills this gap in the literature. Micro structural study revealed that DMLS-produced Ti6Al4V has a porous and fine grain structure (with mostly α′ phase) without any crack formation due to the controlled parameters during DMLS. Corrosion tests were conducted in simulated body fluid as an electrolytic media, while fibroblast cell lines were used to evaluate the cell viability. Compared to the conventional cast product, DMLS-produced Ti6Al4V alloy exhibited significantly higher porosity (4.8 times), scratch resistance (23.25%), wear resistance (11.53%), corrosion resistance (16.56%), and cell growth. (4.37%), thus making it a more suitable alloy for implants.

Machine learning-augmented modeling on the formation of Si-dominated Non-β″ early-stage precipitates in Al-Si-Mg alloys with Si supersaturation induced by non-equilibrium solidification

Recent experiments have shown that Al-Si-Mg alloys solidified under high cooling rates may lead to the nucleation of Si-enriched clusters that are remarkably different from the conventional Mg-Si co-clusters (e.g. β″ particles), and yet the responsible mechanism remains to be elucidated. Here we tackle the problem using a multiscale modeling framework that integrates atomistic modeling, energy landscape sampling, and lattice-based kinetic Monte Carlo (kMC) simulation. The migration energy barriers for vacancy-mediated diffusion amid complex local chemical environments are predicted on-the-fly using a surrogate machine learning model. We discover that the actual vacancy-Si migration barriers are much lower than those assumed in the classic linear interpolation approximation. Such a strong deviation from conventional wisdom, in conjunction with differing Si solute composition, can lead to a great variety in the nucleated early-stage precipitates. More specifically, a high-level supersaturation of Si solute (i.e.xSi/(xSi+xMg)>0.75) would lead to an unexpectedly high enrichment of Si in the nucleated clusters with the Si:Mg ratio up to 5∼6; while at a lower-level supply of Si solute the Mg-Si co-clusters (i.e. Si:Mg ratio around 1∼2) are nucleated instead. These findings provide a viable explanation for the diverse types of early-stage precipitates observed in various experiments, from Si-enriched precipitates in high-pressure die cast Al alloys to β″ particles in conventional casting and/or heat-treated alloys. The implications of our findings are also discussed.

Thermal features and its effect on the properties of AISI 4140 fabricated by conventional and extreme high-speed laser material deposition

The extreme high-speed laser material deposition (EHLA) process has the potential to enable additive manufacturing for mass production by overcoming the limitations of slow scanning speed in conventional laser material deposition (LMD) processes. Thermal features are the key factors to link process and properties. A sound understanding of process-thermal-property relationships is essential for performance control and process optimization of a deposited component. In this study, we studied the thermal characteristics within a single layer and among layers for continuous processing using the numerical method, and reveal the mechanism of microstructure and hardness changes of AISI 4140 material formed by EHLA and LMD processes through the analysis of thermal properties and temperature history results. The grain size and hardness evolution for both processes during single-layer cladding and continuous forming processes were investigated. The results revealed that the grain refinement effect in continuous LMD processing is stronger than that in EHLA process (from 30.0 μm for single layer to 3.2 μm for multi layers vs. from 18.6 μm for single layer to 2.2 μm for multi layers). Similar hardness values were obtained by LMD and EHLA processes, with mean values of 511 HV and 472 HV, respectively. The yield and tensile strengths of EHLA were superior to the conventional cast material, but inferior to those of the conventional material quenched and tempered at lower temperatures. The enhanced tensile results of EHLA process were found similar to those prepared through conventional method with quench and tempering at 600 °C.

Effect of Cryogenic and Room-Temperature Rolling on the Microstructural Evolution and Mechanical Behavior of Spray-Formed 7055 Al-Zn-Mg-Cu Alloy

This study investigates the effects of room-temperature rolling (RTR) and cryogenic rolling (CR) on the microstructure, mechanical properties, and fracture morphology of spray-formed (SF) 7055 Al-Zn-Mg-Cu alloy, with a focus on the deformation across reductions ranging from 20% to 80%. Utilizing SF as the base processing technique, the study aims to overcome challenges associated with the alloy’s high content during conventional casting, such as segregation, grain coarsening, and the formation of internal defects. The findings indicate that CR significantly enhances the ductility and refines the microstructure of SF-7055 Al alloy compared to RTR, particularly at higher reductions. CR prevents the formation of severe cracks and maintains higher ductility and texture intensity, which are crucial for the demanding applications of this alloy in aerospace and transportation sectors. Microstructural analysis reveals that CR achieves a more uniform deformation, effectively reduces shear band formation, and facilitates the formation of finer and more evenly distributed precipitates due to suppressed solute atom mobility at cryogenic temperatures. Mechanical testing shows that CR enhances strength and hardness at lower reductions by maintaining high dislocation density, which does not annihilate as rapidly as in RTR. Tensile fracture analysis further demonstrates that CR leads to smoother fracture surfaces and fewer macroscopic cracks, indicating a more controlled failure mechanism. This study underscores the potential of cryogenic processing in improving the performance and applicability of high-strength Al alloys, offering significant insights for industrial applications where material reliability and enhanced mechanical properties are critical.

Fabrication of highly flexible biopolymeric chitosan/agarose based bioscaffold with Matricaria recutita herbal extract for antimicrobial wound dressing applications

A flexible biopolymer-based antimicrobial wound dressing has the potential to alleviate the burden of bacterial infections in wounds by enhancing antimicrobial effectiveness and promoting faster wound healing. This study focuses on the development of a highly flexible chitosan-agarose (CS-AG) bioscaffold, incorporating Matricaria recutita chamomile flower extract (CH) through a conventional casting method. The flexible CS-AG bioscaffold's physiochemical properties were confirmed by FTIR, indicating secondary interactions, and XRD, showing its crystalline structure. The addition of CH to the optimized CS-AG bioscaffold resulted in significant tensile strength (17.28 ± 0.33 MPa), distinctive structural morphology (SEM), surface roughness (AFM), contact angle, improved thermal properties (DSC), and enhanced thermal stability (TGA). Furthermore, the CH-infused bioscaffold significantly increased swelling capacity (~81.09 ± 1.74 % over 48 h), and degradation profile (~52 % over 180 h). The release studies of CS-AG-CH bioscaffold demonstrate controlled release of CH with in the bioscaffold at different pH conditions. The bioscaffold demonstrated effective antibacterial activity against S. aureus and E. coli strains. Additionally, cytotoxicity assays indicated that the bioscaffold supports better cell viability and proliferation in fibroblast (NIH 3T3) cell lines. Consequently, this antimicrobial bioscaffold shows promise as a drug release system and biocompatible wound dressing suitable for tissue engineering applications.

The Accuracy of Custom-Made Milled Metal Posts as Compared to Conventional Cast Metal Posts.

The aim of this study was to compare the fitting accuracy of custom-made metal posts and cores fabricated by half-digital and milling technique to that of conventional cast posts fabricated by direct technique. Sixteen extracted single-rooted teeth were endodontically treated followed by post space preparation. A direct resin post and core pattern was made for each tooth and used for the fabrication of two posts (n = 16). Each post resin pattern was digitized with a laboratory scanner and used for the fabrication of a milled cobalt-chrome (Co-Cr) alloy post, while the direct resin pattern, after scanning, was cast in a Co-Cr alloy to produce a cast post. Each post was seated on its respective tooth and evaluated using microcomputed tomography. The following variables were evaluated: total space volume between the post and root canal, the volume and distance of the apical gap between each post and the remaining apical root canal filling, as well as the distance and surface area of the space between the post and lateral root canal wall at four determined points along the length of each post. The results revealed that half-digital and milled posts had a statistically significantly higher total space volume (p < 0.05), apical gap volume (p < 0.02) and distance (p < 0.02), as well as a higher surface area of space between the post and root canal wall at the cervical area as compared to the cast post (p < 0.05). This study demonstrated that the fitting accuracy of cast posts was more accurate than posts fabricated with half-digital and milling technique.

The effect of temperature during plasma nitriding on the properties of IN718 additively manufactured by laser beam powder bed fusion

The IN718 superalloy has become a strategic alloy for applications in critical components in aerospace, oil, and gas, or power generation. Commercially, IN718 is produced by conventional casting processes. However, manufacturing is evolving towards 3D printing, which allows the manufacturing of near-net-shape parts and complex designs, thus optimizing manufacturing steps, reducing production costs, and adding other advantages to the final product. However, high corrosion resistance and mechanical strength are required in applications such as oil and gas, whereas IN718 superalloys have limitations. Surface hardening by applying plasma nitriding can protect against corrosion by increasing mechanical strength and wear resistance. For this, plasma nitriding has been widely applied for surface hardening of IN718; however, little is found on the effects of surface treatments (coating or nitriding) of additively manufactured alloys. The effects of temperature during plasma nitriding on the surface properties of IN718 superalloy 3D printed by the Laser Beam Powder Bed Fusion (LB-PBF) method are reported here. Samples of IN718 fabricated by 3D printing were plasma nitrided at fixed temperatures between 500 and 650 °C in a semi-industrial reactor, their effects are analyzed and correlated with their microstructural characteristics, the mechanical properties at the micro- and nanoscale, and the tribological responses in a pin-on-disk configuration.

A comparative study on nanoscale mechanical properties of CrMnFeCoNi high-entropy alloys fabricated by casting and additive manufacturing

Additive manufacturing (AM) has emerged as a pioneering method for fabricating high entropy alloys (HEAs), yet a comprehensive comparison of their nanoscale mechanical properties with those produced by the conventional casting method remains unexplored. In this study, the nanoindentation was utilized to investigate the nanoscale elastic and plastic characteristics in both additive-manufactured (AM-ed) and as-casted single-phase face-centered cubic (FCC) equiatomic CrMnFeCoNi HEAs. Herein, the hardness, reduced modulus, indentation size effect (ISE), yield strength, fracture toughness, and strain rate sensitivity were comprehensively investigated. The results indicated that the hardness of AM-ed HEA was higher than the as-casted HEA, and the reduced modulus values showed no notable distinction between the two samples. The AM-ed HEA demonstrated simultaneous enhancements in yield strength and fracture toughness compared to the as-casted HEA. The as-casted HEA possessed a more distinct indentation size effect (ISE) than the AM-ed HEA. It was observed that the AM-ed HEA exhibited relatively lower strain rate sensitivity and a larger activation volume. This direct comparison of the mechanical properties and deformation mechanisms from a nanoscale view offers unique insights for optimizing and advancing AM techniques in the fabrication of HEAs.

GEOMETRIC AND FLOW CHARACTERIZATION OF ADDITIVELY MANUFACTURED TURBINE BLADES WITH DRILLED FILM COOLING HOLES

Abstract As designers investigate new cooling technologies to advance future gas turbine engines, manufacturing methods that are fast and accurate are needed. Additive manufacturing facilitates the rapid prototyping of parts at a cost lower than conventional casting, but is challenged in accurately reproducing small features such as turbulators, pin fins and film cooling holes. This study explores the potential application of additive manufacturing and advanced hole drill methods as tools to investigate cooling technologies for future turbine blade designs. Data from computed tomography scans are used to non-destructively evaluate each of the cooling features in the blade. The resulting flow performance of these parts is further related to the manufacturing through benchtop flow testing. Results show that while flow through the entire blade is consistent throughout a full wheel of the additively manufactured cooled blades, flow through smaller regions show larger variations. Shaped film cooling holes manufactured using a high-speed electrical discharge machining method are within tolerance in the metering section but do not expand at the specified angle in the diffuser even though design tolerances are met. In contrast to high-speed EDM, conventional EDM holes are undersized throughout the length of the hole. The roughness results show high levels on thin walls, particularly at the trailing edge and on downskin surfaces. Internal surface roughness is higher than external roughness at most locations on the blade. The results of this study confirm that additive manufacturing along with advanced hole drilling techniques offer faster development of blade cooling designs.

Mechanism of Fe-rich phase supercooling induced by CDS process to regulating microstructure and strengthen properties of Al-Si-Fe alloy

Excessive iron in aluminum alloys forms compounds that weaken their strength and workability. Therefore, controlling the morphology of the Fe-rich phase is vital for developing strong, high-quality aluminum alloys. This research explores the controlled diffusion solidification (CDS) process, an innovative approach designed to optimize the morphology and distribution of the Fe-rich phase, thereby enhancing the alloy properties beyond what conventional methods can achieve. Specifically, the CDS process uniquely modifies the solidification behavior of the alloy, suppressing the growth of the primary Fe-rich phase and enhancing the overall properties. This demonstrating the ability of process to refine microstructural characteristics effectively. The experimental results confirm the presence of primary Si and Al3Fe in the CDS process samples. Consequently, the nucleation of Al3Fe in the precursor alloy leads to the concentration of Fe solutes reduce, impeding the nucleation and growth of the primary Fe-rich phase during the subsequent solidification process. The key factors are temperature difference between two mixed alloy and mass ratio of precursor alloys. The mass ratio influences the precipitation sequence of the precursor alloys, while the difference of temperature and concentration induces the undercooling necessary for nucleation. The study reveals that an optimal mass ratio of 4:1 in the CDS process achieves the best mechanical properties with a 73.78 % increase in ultimate tensile strength (UTS) and a 107.77 % increase in elongation (UL) compared to conventional casting. The findings provide a theoretical basis for controlling the Fe-rich phase evolution, significantly augmenting the performance of Al-Si-Fe alloys. The findings not only enhancing the optimizing fundamental reactions in the CDS process for other alloy systems but also enriching the broader field of materials science.

Structure and mechanical properties of low-density AlCrFeTiX (X = Co, Ni, Cu) high-entropy alloys produced by spark plasma sintering

In this study, low-density (< 6 g/cm3) AlCrFeTiX (x = Co, Ni, Cu) high-entropy alloys were produced by mechanical alloying and spark plasma sintering (SPS), and their structures and mechanical properties after SPS and annealing at 1000 °C for 24 h were reported. Both after SPS and annealing, the AlCrFeTiX (x = Co, Ni, Cu) alloys consisted of an L21 matrix phase with embedded bcc and C14 Laves phase particles. All the alloys had a nano-sized structure after SPS that retained in the AlCrFeTiCo and AlCrFeTiNi alloys after annealing. In the AlCrFeTiCu alloy, the annealing led to a coarsening, with an increase in the size of structural constituents above 1 μm. Compression tests showed that the AlCrFeTiX (x = Co, Ni, Cu) alloys after SPS were brittle at 25 °C, but the AlCrFeTiCo alloy exhibited the highest peak strength of 3792 MPa. At 600 °C, the AlCrFeTiCo alloy after SPS also demonstrated the best performance, with the yield strength, peak strength, and plastic strain of 1960 MPa, 2121 MPa, and 1.8 %, respectively. The annealing did not eliminate the room-temperature brittleness, but improved the mechanical properties at 600 °C. The AlCrFeTiCo alloy showed a 15 %-increase in yield strength (2264 MPa) and more than 2.5 times higher compressive plasticity (4.7 %). The AlCrFeTiNi alloy became more ductile (1 %) and stronger (2200 MPa). For the AlCrFeTiCu alloy, the annealing had a negative effect that resulted in a halved plasticity at 600 °C. The AlCrFeTiCo and AlCrFeTiNi alloys after annealing showed record-high specific yield strength values at 600 °C, which were 383 and 371 MPa*cm3/g, respectively. With these values, the AlCrFeTiCo and AlCrFeTiNi alloys outperformed all the low-density medium-/high-entropy alloys available in literature to date obtained both by SPS or conventional casting. The structure formation and mechanical properties, as well as the response of these features to annealing, were extensively discussed.

Achieving significant grain refinement efficiency in Mg-Al alloys via a GNP@MgO composite refiner

Master alloys containing Zirconium (Zr) serve as effective grain refiners in most commercial cast magnesium (Mg) alloys. However, their efficacy is diminished in Mg–Al series alloys due to the formation of Al–Zr compounds. In this work, a novel Mg-GNP@MgO master alloy was prepared utilizing the in-situ reaction between CO2 and Mg. The grain refinement efficiency of this composite inoculation on Mg–9Al alloys was systematically investigated using SEM-EBSD, HRTEM observations, Density Functional Theory (DFT), and Sharp Interface Model (SIM) calculations. The findings suggest that the composite grain refiner (GNP@MgO) exerted a notable refining influence on Mg–9Al alloy. Through the conventional casting process, the average grain size was refined to approximately 13 μm upon the addition of 3 vol% GNP@MgO, achieving a grain refinement efficiency of 90 %. The enhanced refining efficiency arises from the synergistic control over the nucleation and growth processes of α-Mg grains, facilitated by GNP@MgO particles. This process includes improved heterogeneous nucleation, triggered by the newly formed Al4C3 phases through the interaction between GNPs and Al element, followed by the limited expansion of α-Mg grains induced by the nano-sized MgO particles. The MgO particles predominantly gather around grain boundaries to establish stable nano-coating layers, thereby exerting a substantial Zener pinning effect. The pinning role played by the MgO nanoparticles was also verified by a sharp interface model. The findings in this work not only carve out a new avenue for the grain refinement of cast Mg–Al alloys but also inspire fresh perspectives for the development of novel grain refiners.

Achieving exceptional high-temperature strength in a cast Mg alloy via LPSO honeycomb shell

Conventional casting Mg alloys tend to lose strength quickly when exposed to elevated temperatures (200–300 °C). Here, we report a cast Mg alloy decorated by honeycomb LPSO structure via high pressure die casting, with an impressive strength of 191 MPa at 300 °C, exceeding all traditional cast Mg based alloys and common Al-Si alloys. Such remarkable strength ascribes to the strong geometric confinement of the LPSO cellular shell to grain boundaries and dislocations, coupled with extra strain hardening derived from <a> dislocation interactions with stacking faults. In addition, non-basal <a> and <c> dislocations avoid macro-plastic instability at high strains.

Influence of Different Undercut Depths of Clasp Fabricated by Selective Laser Melting on Retentive Force.

The purpose of this study was to investigate the influence of undercut depths on abutment teeth regarding the retentive force of clasps fabricated through selective laser melting (SLM), and to compare them with conventional cast clasps. Akers clasps made of cobalt chromium alloy were fabricated using the SLM method (SLM), and the retentive forces were compared with clasps made with the conventional cast method (Cast). Three undercut amounts (0.25 mm, 0.15 mm, and 0 mm) were applied on the abutment tooth. The specimens were subjected to 10,000 repetitive insertion/removal cycles. SLM-0.15 showed slightly lower initial retentive force than the Cast specimens, it remained within an acceptable range. During insertion/removal test, the SLM-0.15 specimen showed a significant difference between the initial retentive force and the retentive force after 5,000 cycles, indicating that SLM-0.15 was the least likely to change in retentive force within the parameters established in this study. The inner clasp surface on the SLM groups had higher surface roughness before testing compared to the Cast specimen. Akers clasps fabricated by SLM demonstrated optimal initial retentive forces with smaller undercuts than conventional Cast clasps, and the retentive forces changed less with repetitive insertion/removal.

Comparative Studies of the Properties of Copper Components: Conventional vs. Additive Manufacturing Technologies

This article presents a comparative analysis of the crucial physical properties of electrically conductive components made of pure copper, produced by various additive manufacturing technologies such as binder jetting (BJ) and direct metal laser sintering (DMLS). The comparison concerned the assessment of critical parameters important from the application point of view, such as: electrical conductivity, hardness, yield point, microstructure and the occurrence of internal material defects. Same-sized components made in a conventional casting and subtractive method (machining) were used as a reference material. Comprehensive tests and the comparison of a wide range of parameters allowed us to determine that among the selected methods, printing using the DMLS technique allowed for obtaining arcing contact with mechanical and electrical parameters very similar to the reference element. Therefore, the obtained results showed the possibility of using the copper elements made by additive manufacturing for the switching and protection devices used in electrification and energy distribution industrial sectors.

Effect of Ceramic Veneering on the Microstructure of Pre-sintered Cobalt-Chromium, Compared to Pre-sintered Zirconia and Conventional Cast Alloys.

Objectives: We aimed to evaluate ceramic-alloy interface and emphasize the alteration of alloy microstructure after ceramic layering. Materials and Methods: Thirty-two discs made from a ceramic-alloy combination of pre-sintered cobalt-chromium (CoCr), cast CoCr, cast nickel-chromium (NiCr), or pre-sintered zirconia were prepared with eight discs in each group. Four specimens were examined as manufactured and four were ceramic-layered. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-Ray diffractometer (XRD), and an atomic force microscope were used for analysis. Non-layered specimens received ceramic fire-heating without adding any ceramic. Alloy microstructure was compared before and after ceramic veneering or heating within the same group. Mean differences in grain size and surface roughness were compared among groups. P<0.05 was considered significant. Results: SEM showed a close bonding interface between alloys and ceramics. EDX demonstrated differences compared to the manufacturer's composition. Ceramic-layering reduced grain size for both milled alloys (P<0.05), whereas grain size increased in cast groups (P=0.011). Heat treatment did the same for the CoCr groups (P=0.013). Ceramic veneering increased the surface roughness of the cast CoCr (Gi) (P=0.029) and NiCr (Wi) (P=0.005) groups, whereas zirconia roughness average (Ra) showed a slight decrease (P=0.282). XRD showed no differences among zirconia, NiCr, and milled CoCr groups before and after veneering. Crystallite size differed between monoclinic and tetragonal phases in zirconia. Conclusion: The study highlights that ceramic-layering induces significant microstructural changes in alloys, enhancing bonding potential and mechanical stability. Pre-sintered materials show a fine homogeneous surface, optimizing ceramic adherence and potentially improving clinical outcomes.

Bond strength and interfacial analysis of six CoCr alloys made by conventional casting and selective laser melting.

To investigate the effects of the elemental composition and the manufacturing process of cobalt chromium-molybdenum (CoCr-Mo), cobalt chromium-tungsten (CoCr-W), and CoCr-Mo-W alloys on metal-ceramic bond strength. Six CoCr-based alloys were included in this study, a were classified into three different groups depending on their elemental composition (Ν = 10, for each group). The first group had molybdenum (Mo) as the third alloying element, the second group contained tungsten (W) (without Mo), and the third group included both alloying elements. The groups were further divided by the manufacturing process (casting or selective laser melting, SLM). Interfacial analysis was carried out using backscattered electron imaging (BEI) and energy-dispersive X-ray microanalysis (EDX) operating in line scan mode. The metal-ceramic bond strength was tested by a 3-point bending test according to the ISO 9693 requirements. The fracture mode of all specimens was examined under a stereomicroscope. The bond strength results were statistically analyzed by 2-way ANOVA and Tukey's multiple comparison post hoc test (a = 0.05). A continuous interface with the porcelain was found without pores, debonding areas, or other defects. Of the major elements found at the interface, Co showed the highest diffusion rate, while titanium (Ti) had the lowest diffusion rate. No statistically significant differences were identified in metal-ceramic bond strength either among materials or between manufacturing processes. The fracture mode was found to be cohesive for all specimens. The metal-ceramic bond strength is independent of the current CoCr alloy type and manufacturing process when comparing conventional casting and SLM. Interfacial analysis revealed no differences between the tested groups.