Cr Mo Alloy Research Articles

Constitutive Characteristics, Microstructure, and Texture Evolution of As‐Cast 42CrMo Alloy in Nonisothermal Multipass Compression

The nonisothermal multipass deformation behavior of as‐cast 42CrMo alloy was studied with declining temperature, constant pass strain, varying strain rate, and interval time. The stresses are used to develop the constitutive model. As the finishing temperature increases from 990°C to 1070°C, the stress decreases gradually and the softening effect increases, which results in a large grain size and inhomogeneous microstructure. The low angle grain boundaries transform into high angle grain boundaries through absorbing dislocations. The noticeable stress softening in a high strain rate is attributed to the thermal softening, dynamic recovery, and dynamic recrystallization. The thermal softening is no longer considered to be the main interpass softening mechanism at a low strain rate. The interval time has a negligible effect on the stress, but the significant changes in grain size and texture component are caused by the interpass softening. The average grain size is approximately 40 μm, and the distorted grain boundaries and small fine grains are found in the interval times of 0.5–5 s, implying the dynamic recovery and grain growth. The near {001}<110> and {110}<112> orientation exerts an important influence on the grain refinement.

Improvement of carbon segregation in cast bloom and heredity in hot-rolled bar

In this study, the effect of mechanical soft reduction on carbon segregation in the continuous casting of 300 × 400 mm 42CrMo alloy structural steel blooms was comparatively investigated by adjusting the casting speed, which was systematically optimized through numerical simulation. When the casting speed is 0.60 m · min−1, during the soft reduction process, the central solidification structure of the bloom becomes dense, and carbon segregation is improved. Moreover, the distribution of carbon in the samples before and after rolling was analyzed. Combined with the soft reduction process, the uniformity of carbon across the cross section of the bloom /bar distinctly improved for casting speeds of 0.50 m · min−1, 0.55 m · min−1 and 0.60 m · min−1, this was predominantly reflected in the core areas. The effective segregation length proportion of the bloom and rolled bar is approximately 40%. This phenomenon fully verifies the heredity characteristics of the elements in the rolling process.

Effects of Nb/Ti additions and heat treatment on the microstructure evolution and hardness of as-cast and directionally solidified NiAl–Cr(Mo) alloy

The effects of the addition of Nb and Ti and heat treatment on the microstructure evolution and hardness of the as-cast and directionally solidified NiAl–Cr(Mo) alloy were studied. Nb mainly solubilizes in the Cr(Mo) phase while Ti basically solubilizes in the NiAl phase. Precipitated phases of Cr2Nb and Ni2AlTi are formed and mainly distributed at the cell boundary. With the increasing Nb content, the primary Cr(Mo) phase increases significantly and does not show dendritic morphology. The eutectic coupled growth is suppressed and the lamellar microstructure becomes irregular. Fully eutectic microstructure with no primary Cr(Mo) phase is obtained in the directionally solidified NiAl–Cr(Mo)–Nb and NiAl–32Cr–6Mo–1Ti–1Nb alloys while dendrites + eutectic is observed in the directionally solidified NiAl–32Cr–6Mo–3Ti–3Nb alloy. After heat treatment, Nb and Ti are redistributed. The eutectic microstructure becomes relatively uniform and the precipitated phases become fine and dispersed. The addition of Nb and Ti can increase the hardness of the alloy due to the solid solution strengthening and precipitation strengthening. As the Nb content increases, the hardness further increases. The hardness of the directionally solidified alloys is higher than the as-cast alloys attributing to the regular microstructure. After heat treatment, the hardness of the all alloys decreases due to the varying microstructure morphology and phase distribution, especially the coarsening of NiAl precipitates and the existence of dislocations in Cr(Mo) phase.

Osseointegration of additive manufacturing Ti–6Al–4V and Co–Cr–Mo alloys, with and without surface functionalization with hydroxyapatite and type I collagen

The introduction of additive manufacturing (AM) technologies has profoundly revolutionized the implant manufacturing industry, with a particularly significant impact on the field of orthopedics. Electron Beam Melting (EBM) and Direct Metal Laser Sintering (DMLS) represents AM fabrication techniques with a pivotal role in the realization of complex and innovative structure starting from virtual 3D model data. In this study, Ti–6Al–4V and Co–Cr–Mo materials, developed by EBM (Ti-POR) and DMLS (Co-POR) techniques, respectively, with hydroxyapatite (Ti-POR + HA; Co-POR + HA) and type I collagen (Ti-POR-COLL; Co-POR-COLL) coatings, were implanted into lateral femoral condyles of rabbits. Osseointegration process was investigated by histological, histomorphometrical and microhardness evaluations at 4 and 12 weeks after implantation. Both Ti–6Al–4V and Co–Cr–Mo implants, with or without HA and COLL coatings, demonstrated good biocompatibility. As expected, HA coating hastened bone-to-implant contact (BIC) process, while collagen did not significantly improved the osseointegration process in comparison to controls. Regarding newly trabecular bone formation (B.Ar/T.Ar), Co-POR presented the highest values, significantly different from those of Co-POR-COLL. Over time, an increase of BIC parameter and a decrease of B.Ar/T.Ar were detected. Higher mineral apposition rate was observed for Ti-POR and Co-POR in comparison to Ti-POR-COLL and Co-POR-COLL, respectively, at 12 weeks. The same behavior was found for bone formation rate between Co-POR and Co-POR-COLL at 12 weeks. In conclusion, the AM materials guarantee a good osseointegration and provide a suitable environment for bone regeneration with the peculiarity of allowing personalized and patient-specific needs customization to further improve the long-term clinical outcomes.

On the irradiation tolerance of nano-grained Ni–Mo–Cr alloy: 1 MeV He+ irradiation experiment

The irradiation damage behavior was studied in the nano-grained Ni–Mo–Cr alloy (nano-grained GH3535), which was irradiated by He ion to various dose. The evolution of defects and hardness changes are characterized by transmission electron microscopy and nanoindentation to explore the irradiation tolerance of the nano-grained GH3535 and the coarse-grained GH3535 (annealed GH3535), where the later was chosen as reference material to make comparison with nano-grained GH3535. The results show that though both the average size and number density of He bubbles increase with an increase in the irradiation dose, the smaller volume fraction is found in the nano-grained GH3535 compared with the coarse-grained GH3535 under the same irradiation condition. This indicates that the nano-grained GH3535 possess better irradiation swelling resistance than the coarse-grained GH3535. However, the increase in the hardness of the nano-grained GH3535 is more significant than in the coarse-grained GH3535 under the same irradiation dose. This suggests stronger irradiation-induced hardening of the nano-grained alloy comparing to coarse-grained alloy, due to the impeding effect caused by grain boundaries decorated with He bubbles. This study provides insight into the design of irradiation-tolerant nickel-based alloys for nuclear industry applications.

Additive manufacturing of a martensitic Co–Cr–Mo alloy: Towards circumventing the strength–ductility trade-off

Abstract A Co–Cr–Mo alloy with predominantly martensitic structure was prepared by selective laser melting (SLM), where the amount of martensite formed in the SLM specimens is much larger than in the cast samples which can be ascribed to the high density of internal defects such as dislocations and SFs. We observe a hierarchical microstructure spanning over different length scales, consisting of remelted zones and track core regions at the macro-scale, regions with elongated columnar grains and equiaxed grains at the micro-scale, martensitic laths at the submicron-scale, and a high density of dislocations and stacking faults at the nano- and atomic scale. The hierarchical microstructure leads to the outstanding tensile properties of the as-prepared SLM and SLM annealed samples (with yield strength, ultimate tensile strength and fracture strain of ~ 735 MPa, ~ 1211 MPa and ~ 12.8%, and ~ 893 MPa, ~ 1214 MPa and ~ 13.8%, respectively). The mechanisms determining the strength and ductility are discussed in terms of the hierarchical microstructure and internal defects. The cellular structure with a high density of dislocations along their boundaries and the martensitic structure are the reasons for strengthening, while the hierarchical microstructure helps to obtain appropriate ductility. Furthermore, martensitic transformation induced plastic bending of the residual FCC plates was confirmed, which is helpful to maintain the different plastic strain between the heterogeneous structure. The development of the martensitic structure in this Co–Cr–Mo alloy by SLM and its characteristic hierarchical microstructure are promising features for material design and application of high-strength materials with improved strength‒ductility tradeoff.

Reduction in anisotropic response of corrosion properties of selective laser melted Co–Cr–Mo alloys by post-heat treatment

ObjectivesThe application of selective laser melting (SLM) to dentistry has been rapidly expanding; however, SLM-processed parts possess orientation-dependent properties (i.e., anisotropy) that can affect the long-term reliability of the dental prostheses. This study aimed to evaluate the anisotropic corrosion response of SLM-processed Co–Cr–Mo alloys under various heat treatments. MethodsSamples fabricated via SLM along the horizontal plane (x-y plane) and vertical plane (x-z plane), with respect to the build direction, were subjected to various heat treatments. The resulting microstructures of the samples were characterized, and their corrosion properties were evaluated using anodic polarization and immersion tests. ResultsAll samples showed similar transpassive behavior of the polarization curves. However, the immersion tests showed that the as-built x-z plane samples released significantly more metal ions than those fabricated on the x-y plane because of the larger area of preferentially corroded molten pool boundaries (MPBs) in the x-z plane samples. Our results further demonstrated that the heat treatments eliminated the MPBs, resulting in isotropic corrosion properties. However, excessive heat treatment at high temperatures induces the formation of coarse precipitates, resulting in a less-protective passive film. SignificanceThe post-build heat treatments at temperatures that eliminate the MPBs are effective in reducing anisotropic corrosion behavior, and the lowest possible temperature is suitable for reducing the amount of released metal ions. These findings are expected to facilitate the application of SLM in dentistry to allow fast and precise production of prosthetic devices.

Portevin-Le Chatelier effect, twinning-detwinning and disordering in an aged Ni–Cr–Mo alloy during large plastic deformation

Abstract Portevin-Le Chatelier (PLC) effects, twinning-detwinning and disordering phenomena in long-range ordered (LRO) phase strengthened Ni–Cr–Mo alloys during hot compression are reported and investigated. The results reveal that the PLC effects with type-C serrations occur in the solution-treated and aged alloys, and that the Pt2Mo-type LRO phase can increase the serration amplitude at the early stage of deformation. Only after the early stage of deformation, the twinning of aged alloy can be activated. However, the deformation twin and the Pt2Mo-type LRO phase are not stable during the severe deformation. The potential disordering process of the LRO phase is provided as the slipping of the dislocation on the two valid {111} slip systems. The occurrence of the steps on the twin boundaries of the remanent deformation twins reveals that the detwinning mechanism is likely the dislocation-twin boundary interaction.

A study on the bacterial adhesion of Streptococcus mutans in various dental ceramics: In vitro study

AbstractStreptococcus mutans(S. mutans) has been identified as a major etiologic agent of human dental caries and forms a significant proportion of oral streptococci in carious lesions. This study investigates the correlation of surface properties (effect of contact angle [CA] and free surface energy) on three restorative materials (zirconia, nickel–chromium–molybdenum alloy and composites) used in dental prosthetics with bacterial adhesion toS. mutans. Ten samples of each material (zirconia, nickel–chromium–molybdenum alloy and composites) of 8 mm diameter and 2.5 mm thickness were used. Aqueous CA measurements, free surface energy and bacterial adhesion to the sample surfaces were performed. Bacterial adhesion is determined by planting samples in the blood agar cultures and using an electron microscope (scanning electron microscopy [SEM]). The highest values of bacterial adhesion are found in composites, followed by the metal alloy, while the lowest values are observed in zirconia. Measurements show that zirconia has 17 bacteria; Ni–Cr–Mo alloy has 65, while the composite has 80 bacteria. The composites showed the highest degree of bacterial adhesion, compared to the other investigated materials, which correlates with the free surface energy of the samples (24.31 mJ/m2for zirconia, 31.78 mJ/m2for Ni–Cr–Mo alloy and 48.82 mJ/m2for the composite).

The Effect of Microstructure and Welding-Induced Plasticity on the Strength of Ni–Mo–Cr Alloy Welds

The mechanical performance of a Ni–Mo–Cr (GH3535) alloy weldment, produced using a matching filler metal, was assessed and compared to the surrounding parent metal. Ambient-temperature mechanical characterisation included hardness testing, small punch testing and uniaxial tensile testing, while a crystal plasticity finite element model was used to assess the impact of crystallographic texture on the mechanical properties. Despite the similar chemical composition, the weld metal exhibited superior strength and ductility to that of the parent metal. The higher strength was primarily attributed to the high dislocation density in the weld metal imbued by the welding-induced thermo-mechanical loading. In contrast, the ductility difference was attributed to M6C carbide stringers in the parent metal that initiated fracture at lower strains than for the weld metal, with the latter containing much finer, well-dispersed M6C carbides.

Twinning during deformation in a Pt2Mo ordered phase strengthened Ni–Cr–Mo alloy

Twinning during deformation in a Pt2Mo ordered phase strengthened Ni–Cr–Mo alloy

Corrosion Characteristics of Typical Ni–Cr Alloys and Ni–Cr–Mo Alloys in Supercritical Water: A Review

The corrosion of supercritical water system materials under high-temperature and high-pressure conditions exists widely, which may result in the serious damage of the supercritical water reactor. T...

Corrosion Behavior of a Ni–Cr–Mo Alloy Coating Fabricated by Laser Cladding in a Simulated Sulfuric Acid Dew Point Corrosion Environment

For this study, aimed at proposing a potential direction to prevent sulfuric acid dew point corrosion, a Ni–Cr–Mo alloy Hastelloy C22 coating was fabricated by coaxial laser cladding technology. The phase composition, microstructure, and corrosion behavior in a simulated sulfuric acid dew point corrosion environment were investigated and compared with a Hastelloy C22 alloy, a titanium alloy TC4, and 09CrCuSb steel (ND). The results showed that the phase composition of the C22 coating is essentially similar to that of the C22 alloy, consisting of a γ-Ni solid solution and Ni6Mo6C1.06. The finer microstructure of the C22 coating mainly contains eutectic and dentrite, presenting a typical solidification feature of laser cladding. The corrosion resistance of the C22 coating is very close to that of the C22 alloy, and outclasses that of TC4 and ND. The corrosion behavior of the C22 coating is intergranular corrosion resulting from the segregation of molybdenum, chromium containing corrosion products, and smaller anode micro-batteries.

Laves Phase Formation and Segregation of Nb in Ni–Cr–Mo Superalloy over 316L by Hot Wire (HW) TIG Cladding Process

The Ni-based alloys are widely used in power plant components such as boiler and piping systems that require good creep strength and resistance to corrosion. The present study focuses on metallurgical and mechanical properties of Ni–Cr–Mo (ERNiCrMo-3) alloy cladded over 316L plate by hot wire TIG process. This alloy is prone to microfissuring and also reduced corrosion resistance due to microstructural changes caused by weld solidification. The microstructure and phasic characterization were identified using scanning electron microscopy and X-ray diffraction techniques. From the microstructural observation, it was observed that Nb present in Ni–Cr–Mo alloy tends to segregate during solidification of weld thereby promoting the Nb-rich Laves phase formation. The growth of dendrites enhanced the segregation of Nb. The coarse dendritic microstructure was due to the effect of high heat input that decreases solidification rate near the interface zone. Dimples and quasi-cleavage fracture morphology was observed on the fractured samples of the tensile test. The resistance to corrosion was evaluated using potentiodynamic polarization method using 3.5 wt% NaCl solution. The results confirmed that Ni–Cr–Mo alloy acts as an efficient clad for 316L substrate from corrosion attack.

Tribological behavior of NiAl-based intermetallic compounds in artificial seawater

The solid-lubricating material is a promising candidate for the tribo-pairs exposed in a seawater environment. In this paper, the tribological properties of NiAl-based intermetallic compounds in the seawater were investigated. The results revealed that NiAl–Cr(Mo)–Ag alloy exhibits the lowest friction coefficient (~0.1) and wear rate (~10−7 mm3/Nm) compared to NiAl and NiAl–Cr(Mo) alloys, which is attributed to the solid-lubricating action of Ag. NiAl–Cr(Mo) alloy displays the highest friction coefficient, resulting from the severe abrasive action of the tribo-pair. The wear features of NiAl and NiAl–Cr(Mo) alloys are delamination and plowing effect, respectively. However, the worn surface of NiAl–Cr(Mo)–Ag alloy is almost smooth. Abrasive wear is dominated by the wear mechanisms of NiAl-based intermetallic compounds, while corrosion wear is mild.

A promising post-additive manufacturing surface modification for tailoring gradient nanostructure and harmonic structure in Co–Cr–Mo alloy

In this paper, I tailored a Co–Cr–Mo alloy prepared by additive manufacturing (AM) method to contain both the gradient nanostructure (GN) and harmonic structure (HS) by UNSM (ultrasonic nanocrystal surface modification) at 25 and 500 °C, respectively. The main objective is to characterize the microstructural changes and to evaluate the mechanical properties of GN and HM. Temperature of UNSM played a significant role in controlling the microstructure and strength of GN and HM, where the UNSM-treated at 500 °C sample demonstrated higher strength than those of the as-AM and UNSM at 25 °C samples.

Structure and mechanical performance for TiAlN films that are grown with a low Al composition

An orthogonal array L9 (34) is used with the grey Taguchi design to optimize the performance of TiAlN films that are grown by direct current magnetron co-sputtering, using a low Al concentration. The structure, mechanical performance and the cutting properties of a coated TiAlN tool for which the films are deposited using various parameters are determined. For the optimal deposition conditions, the (111) diffraction peak intensity increases, which demonstrates an improvement in the crystallinity of the TiAlN films. A TiAlN film coated cutter insert is used for the dry milling of a Cr-Mo alloy steel workpiece and it is shown that the tool flank wear decreases and there are fewer surface defects proved. In the confirmation cutting tests the surface roughness is decreased by 26.08% and the flank wear is 16.15% less. The TiAlN films exhibit good mechanical performance, using grey relational analysis, the improvement rate in hardness H is 14.74%, in friction coefficient is 45.88%, in elastic modulus E is 9.56%, in H/E is 9.09% and in H3/E2 is 25.92%.

A study on wettability and formation of intermetallic phase between Co–Cr–Mo alloy and Sn-Solder used as a potential under bump metallization for flip-chip packages

The wettability and formation of intermetallic compounds (IMCs) formed between a Co–Cr–Mo-based alloy and Sn-solder metal were investigated using the reflow soldering method. Soldering was conducted in an electric furnace in separate experiments at temperatures of 533, 553, 573, 623, and 673 K for 600 s. The morphology of the intermetallic layer formed at the Co–Cr–Mo-based/Sn-solder interface was characterized by scanning electron microscopy (SEM). The chemical composition and phase of the formed intermetallic layer were analyzed by electron probe microscopic analysis (EPMA) and X-ray diffraction analysis. Wettability analysis indicated that the soldering temperature influenced the wettability. With increasing soldering temperatures, the spreading factor increased, whereas the contact angle decreased. The intermetallic layers were found in triples in the intermediate zone between the solidified Sn-solder and the Co–Cr–Mo-based substrate. The thickness of the intermetallic layers increased in proportion with increasing soldering temperature. The EPMA analysis indicated only two IMCs formed at the interface of the joint at all of the investigated soldering temperatures, although three interfacial layers were observed by SEM analysis. The Sn-richer phase, Co(Cr,Mo)Sn2, formed adjacent to the Sn-solder matrix, whereas the Co(Cr,Mo)Sn was found near the Co–Cr–Mo-based substrate. The nanoindentation measurement revealed that the formed Co(Cr,Mo)Sn2 and Co(Cr,Mo)Sn IMCs possessed lower hardness values compared to the Sn–Cu intermetallic systems.

Optimization the working parameters of as-forged 42CrMo steel by constitutive equation-dynamic recrystallization equation and processing maps

42CrMo steel belongs to low-alloy medium carbon steel and also belongs to ultra-high-strength steel. In this study, thermal compression tests (800°C - 1200°C, 0.01s-1 - 10s-1) and subsequent calculations proved that many material constants of 42CrMo alloy steel have a similar functional relationship with Z parameter: Material constants=a*Zb. The thermal processing maps under strains of 0.2, 0.4, 0.6 and 0.8 were established, and the practical application of the processing maps was verified in combination with metallographic diagram analysis. The optimum thermal processing parameters range of the material was obtained: the temperature range of 1000°C - 1125°C and the strain rate range of 3.16 s-1 - 10s-1.The dynamic recrystallization volume fraction model and grain size model of the material were established, and the typical sigmodal curve was obtained. The hot workability and recrystallization behavior of 42CrMo were further analyzed.

Effect of processing parameters on the microstructure and mechanical properties of Co–Cr–Mo alloy fabricated by selective laser melting

Selective laser melting (SLM) is an additive manufacturing process that builds metal components according to computer-aided design (CAD), selectively fusing and consolidating metal powders one layer at a time. This study systematically investigates the influence of various laser conditions on the microstructure and mechanical properties of Co–Cr–Mo alloy fabricated by SLM. Hot isostatic pressing (HIP) was applied after SLM to further densify the fabricated components, and their microstructures and mechanical properties were compared with those of as-built samples. Parts with relative density of ∼97.17% were obtained with a high-energy laser density and double laser scanning, and subsequent HIP effectively eliminated the majority of pores. X-ray diffraction revealed that γ and ε phases co-existed owing to the high solidification rate during SLM. Directional columnar grains and fine cellular dendrites that were parallel and normal, respectively, to the build direction were observed. Although variations in microstructure resulting from different as-built samples were insignificant, the mechanical properties remarkably changed. The improved mechanical behavior was attributed mainly to increased densification and grain-boundary strengthening. However, the HIP treatment increased the tensile ductility and reduced the yield strength, as a result of the increase in grain size. The tension-fractured surface suggests that mostly quasi-cleavage brittle fracture took place in the SLM-processed parts.