Response of MC3T3-E1 osteoblast cells to the microenvironment produced on Co–Cr–Mo alloy using laser surface texturing

Osteoblast responses to Co–Cr–Mo alloy depend on not only the chemistry of alloy but also the physical properties of alloy surface, such as its microtopography and roughness. This study was undertaken to examine changes in cell adhesion, morphology, differentiation and gene expression during osteoblast interaction with different textured Co–Cr–Mo alloys. With laser surface texturing, three kinds of textured surfaces were fabricated. It showed that the microenvironment processed by laser surface texturing leads to an increase in surface roughness and DMEM contact angles of samples. Adhesion and differentiation tests demonstrated that osteoblast cells can discriminate surfaces with different roughness and surfaces with comparable roughness but different topographies such as triangle, circle and square textures. Morphological characteristics obtained by SEM imaging showed that osteoblast cells are elongated and are in polygonal shape on the textured surface. OPG/RANKL mRNA expression studies showed a significant and marked decrease in RANKL gene expression on the square-textured surface; by contrast, the ratio of OPG/RANKL showed a significant increase. These results indicate that Co–Cr–Mo surface textures affect osteoblast proliferation, morphology and gene expression; the microenvironment of implant should be considered in the future design.     

The microstructure and mechanical properties of prolonged and lower temperature aged Fe–Ni–Mn–Mo–Ti–Cr maraging steel

In this study, the microstructure and mechanical properties of Fe–Ni–Mn–Mo–Ti–Cr maraging steel at low temperature and prolonged aging condition were investigated. Optical and scanning electron microscopy examinations, tensile and hardness tests were conducted to study the microstructure, aging behavior and mechanical properties of the cold‐rolled steel. The results showed that aging of cold rolled Fe–Ni–Mn–Mo–Ti–Cr maraging steel resulted in the formation of Mo rich and Ti rich Lave phase precipitates. Existence of many dislocation cores due to cold rolling and subsequently, low temperature aging caused to formation of uniform distribution of very fine precipitates. The presence of these precipitates increased the yield and ultimate tensile strengths but couldn't improve the uniform tensile ductility. This alloy showed ultra‐high fracture stress of about 1950 MPa with a negligible tensile elongation (about 2 %) at the peak aged condition. The fractographic studies indicated this alloy shows semi‐brittle fracture in the subsequent aging treatment.     

Mechanical and wear performance evaluation of tungsten added Co‐30Cr‐4Mo‐1Ni biomedical alloy with Taguchi optimization

Development of biomaterial with diverse properties (physical, mechanical, wear, and many others) for hip femoral head is one of the most exigent tasks. Improper material often causes component failure during functioning. Therefore, in this study, a series of implant materials containing tungsten of different weight percentages were fabricated by high temperature vacuum casting induction furnace and the physical, mechanical, and wear properties were examined. The proportions were varied from 0 wt. % ‐ 4 wt.% in a cobalt–chromium alloy (Co‐30Cr‐4Mo‐1Ni). The mechanical properties were tested by the micro‐hardness tester and the compression testing machine, while the wear performance was analyzed through a pin‐on‐disc tribometer under different operating conditions at room temperature. Initially in this study, steady state experimental analysis was performed to obtain the volumetric wear loss and coefficient of friction by varying sliding velocity and normal load respectively. Afterwards, the Taguchi experimental design has been conducted to obtain the optimum wear response. Lastly, scanning electron microscopy and atomic force microscopy were utilized to analyze the contour of wear mechanism and 3D surface topography. From the results obtained, it was found that Co‐30Cr‐4Mo‐1Ni‐2 W implant material provides the best combination of the properties for a given application.     

Einfluss einer PVD‐Al‐Zwischenschicht auf die Eigenschaften eines thermisch gespritzten Wärmedämmschichtsystems nach Temperaturwechselbelastung

Thermal barrier coatings (TBC) generally consist of a metallic bond coat (BC) and a ceramic top coat (TC). Co–Ni–Cr–Al–Y metallic super alloys and Yttria stabilised zirconia (YSZ) have been widely used as bond coat and top coat for thermal barrier coatings systems, respectively. As a result of long‐term exposure of thermal barrier coatings systems to oxygen‐containing atmospheres at high temperatures, a diffusion of oxygen through the porous ceramic layer occurs and consequently an oxidation zone is formed in the interface between ceramic top coat and metallic bond coat. Alloying components of the BC layer create a so‐called thermally grown oxides layer (TGO). One included oxide type is α‐Al₂O₃. α‐Al₂O₃ lowers oxygen diffusion and thus slows down the oxidation process of the bond coat and consequently affects the service life of the coating system positively. The distribution of the alloying elements in the bond coat layer, however, generally causes the formation of mixed oxide phases. The different oxide phases have different growth rates, which cause local stresses, micro‐cracking and, finally, delamination and failure of the ceramic top coat layer. In the present study, a thin Al inter‐layer was deposited by DC‐Magnetron Sputtering on top of the Co–Ni–Cr–Al–Y metallic bond coat, followed by thermal spraying of yttria‐stabilised zirconia (YSZ) as a top coat layer. The deposited Al inter‐layer is meant to transform under operating conditions into a closed layer with high share of α‐Al₂O₃ that slows down the growth rate of the resulting thermally grown oxides layer. Surface morphology and microstructure characteristics as well as thermal cycling behaviour were investigated to study the effect of the intermediate Al layer on the oxidation of the bond coat compared to standard system. The system with Al inter‐layer shows a smaller thermally grown oxides layer thickness compared to standard system after thermal cycling under same conditions.     

Evaluation techniques of metallic biomaterials in vitro

Metals and alloys are widely used as biomedical materials and are important in medicine and they cannot be replaced with ceramics or polymers at present mainly because of their high strength and toughness. Since safety is the most important property of biomaterials, corrosion-resistant materials such as stainless steel, Co–Cr–Mo alloy, commercially pure titanium, and titanium alloys are employed as biomaterials. Evaluation techniques for corrosion with culturing cells, the characterization of reconstruction of surface oxide film, fretting fatigue, cytotoxicity, and biocompatibility are reviewed in this paper. These techniques are original and characteristics in the field of biomaterials that should contribute to the proper evaluations of biomaterials in vitro.     

Measuring bone cell adhesion on implant surfaces using a spinning disc device

The adhesion behaviour of osteoblastic cells on implant surfaces is a main focus during the development of osteoconductive implant surfaces. Therefore, besides cell spreading and proliferation on surfaces the adhesion strength of cells to the substrate is of high interest. There are different approaches to determine cell adhesion but only few quantitative methods. For this purpose, we have developed an adhesion device based on the spinning disc principle in conjunction with an inverse confocal laser scanning microscope (LSM). Mirror polished disc‐shaped test samples made of titanium‐ (Ti6Al4V) and cobalt‐alloys (Co28Cr6Mo), as well as stainless steel (316L), were seeded with osteoblasts, stained with a fluorescent dye, at defined radial positions and were incubated for 18 h in cell culture medium (DMEM). After incubation the test samples were placed into the adhesion chamber filled with DMEM. By means of a computer controlled motor the test samples were rotated for 3 min. Using the LSM the detachment of the cells at defined radial positions was determined and the cell count was recorded before and after rotation with the help of imaging software. An average shear stress of 47.1 N/m², 53.2 N/m² and 49.4 N/m² was assessed for the mirror polished Ti6Al4V, Co28Cr6Mo and 316L surfaces respectively. The technique is suitable for studying bone cell adhesion strength on orthopaedic implant materials. Future investigations will focus on different bioactive and anti‐infectious implant surfaces, as well as soluble bioactive factors.     

Investigation of the thermo-stimulated surface segregation in the ternary Co-Cr-Mo alloy by means of Ionization Spectroscopy

Ionization Spectroscopy has been used to study thermo-induced surface segregation in the near-surface region of the ternary Co-Cr-Mo alloy. For the non-annealed alloy the Mo atoms preferred segregation in the outermost layers and Cr atoms segregation in the underlying layers of surface was observed at room temperature. Heating of the alloy promotes increasing of Co concentration and decreasing of Mo concentration in the near-surface region. For the annealed alloy the insignificant Mo atoms segregation on the outermost layers and enrichment with Co and Cr atoms in underlayers are displayed. The present results are compared with several theories of segregation.     

Experimental Study of the Creep Lifetime of the 1.25Cr 0.5Mo Steel Pipes

Abstract: In this paper, physical parameters for the creep constitutive equations of the low alloy ferritic steel 1.25Cr0.5Mo have been determined using experimental data. This alloy is used mostly in power generation and petrochemical industries because of its high temperature creep resistance. Test samples have been obtained from a new super‐heater pipe wall of a steam‐generating boiler in Tabriz Petrochemical Plant according to the ASTM standards. By conducting creep rupture tests for 1.25Cr0.5Mo steel, creep behaviour and creep‐rupture properties were examined for this material. Creep rupture tests have been carried out at four temperatures of 700, 725, 750 and 800 °C, under applied uni‐axial stresses of 30, 35, 40 and 50 MPa. The experimental data have been used to obtain the constitutive parameters using numerical optimisation techniques. Also the temperature and stress dependency of the creep lifetime for this alloy has been investigated using Larson–Miller and Monkman–Grant parameters. The results show good agreement with other test data such as ASTM and API. Finally, these constitutive equations have been used to study the creep behaviour of the super‐heater pipe. The results show that the super‐heater tube has been over designed in terms of the creep lifetime and this is in accordance with the in‐plant observations.     

Effects of the porcelain-fused-to-metal firing process on the surface and corrosion of two Co–Cr dental alloys

The aim of this study was to evaluate the effects of a simulated porcelain-fused-to-metal (PFM) firing process on the surface, corrosion behavior, and cell culture response of two cobalt–chromium (Co–Cr) dental alloys. Two Co–Cr dental alloys were tested—a high and a low molybdenum (Mo)-containing alloys. Before PFM firing, as-cast alloy specimens were examined for their microstructure, surface composition, and hardness. Corrosion behavior was evaluated using electrochemical impedance spectroscopy tests. Mouse 3T3 fibroblasts were exposed indirectly to specimens and MTT cell proliferation assays were performed after 3 and 6 days. The cell culture medium exposed to specimens was analyzed for metal ion release. After firing, similar alloy specimens were examined for the same properties. The tests showed that the PFM firing changed both alloys’ microstructures and hardness values. After PFM firing, the corrosion resistance of the low Mo-containing Co–Cr alloy decreased statistically, which corresponded with a reduction of Cr and oxygen levels in the surface oxides via X-ray photoelectron spectroscopy. Also, the MTT assay of this alloy decreased significantly corresponding with an obvious increase of Co release after the firing. For the high Mo-containing Co–Cr alloy, the surface composition, corrosion resistance, and cell culture response were not significantly changed after PFM firing. The results suggested that the corrosion resistance and biocompatibility of the low Mo-containing Co–Cr alloy decreased after PFM firing, whereas the firing process had little effect on the same properties of the high Mo-containing Co–Cr alloy.     

Surface Modification on Biodegradable Magnesium Alloys as Orthopedic Implant Materials to Improve the Bio-adaptability:A Review

Magnesium(Mg) and its alloys as a novel kind of biodegradable material have attracted much fundamental research and valuable exploration to develop its clinical application. Mg alloys degrade too fast at the early stage after implantation, thus commonly leading to some problems such as osteolysis, early fast mechanical loss, hydric bubble aggregation, gap formation between the implants and the tissue. Surface modification is one of the effective methods to control the degradation property of Mg alloys to adapt to the need of organism. Some coatings with bioactive elements have been developed, especially for the micro-arc oxidation coating, which has high adhesion strength and can be added with Ca, P, and Sr elements. Chemical deposition coating including bio-mimetic deposition coating, electro-deposition coating and chemical conversion coating can provide good anticorrosion property as well as better bioactivity with higher Ca and P content in the coating. From the biodegradation study, it can be seen that surface coating protected the Mg alloys at the early stage providing the Mg alloy substrate with lower degradation rate. The biocompatibility study showed that the surface modification could provide the cell and tissue stable and weak alkaline surface micro-environment adapting to the cell adhesion and tissue growth.The surface modification also decreased the mechanical loss at the early stage adapting to the loadbearing requirement at this stage. From the interface strength between Mg alloys implants and the surrounding tissue study, it can be seen that the surface modification improved the bio-adhesion of Mg alloys with the surrounding tissue, which is believed to be contributed to the tissue adaptability of the surface modification. Therefore, the surface modification adapts the biodegradable magnesium alloys to the need of biodegradation, biocompatibility and mechanical loss property. For the different clinical application, different surface modification methods can be provided to adapt to the clinical requirements for the Mg alloy implants.     

Enhanced surface properties and contact fatigue performance of Cr4Mo4V bearing steel subjected to ultrasonic surface rolling processing

The paper presents the experimental studies on the enhanced comprehensive properties of Cr4Mo4V bearing steel using ultrasonic surface rolling process. Considerable improvements in mechanical properties and rolling contact fatigue performance are achieved in the present study, accompanied by the characterization of surface microstructures. The ultrasonic surface rolling process promotes the formation of fine nanocrystalline structures and nano-sized elongated grains with severe deformation, leading to the increasing residual stress, micro-hardness and high temperatures hardness. The crack propagation and delamination pit in the surface after ultrasonic surface rolling process is inhibited, further enhancing the rolling contact fatigue life of Cr4Mo4V bearing steel.     

医用钴合金表面改性技术的研究进展

钴合金具有优异的生物力学特性、耐磨损性能和耐腐蚀性能,在医学植入领域有着广阔的应用前景,其表面改性技术已成为医用金属材料的研究热点和重点。本文简述了钴合金材料表面改性技术的优势,包括钴合金材料的生物力学特性、耐磨性能、耐腐蚀性能等。同时归纳了钴合金材料因人体体液腐蚀和摩擦磨损会释放出Co、Cr等金属离子而导致生物致敏等问题。在上述基础上,重点综述了近年来钴合金表面改性技术的研究进展,包括离子注入技术、选区激光熔化技术、真空沉积技术。其中,离子注入技术主要包括氮离子注入、钇离子注入、镧离子注入和钛镍离子注入等;选区激光熔化技术主要包括粉层厚度、激光功率、组分含量、扫描方式和扫描速度等;真空沉积技术主要包括物理气相沉积和化学气相沉积。针对不同钴合金表面改性技术,分别从钴合金材料的生物力学特性、耐磨性、耐腐蚀性和生物相容性等方面进行了归纳分析。最后分析了钴合金表面改性的发展趋势,认为钴合金表面改性技术应朝着高生物相容性、无金属离子释放、生物功能化、高耐腐蚀性和高耐磨性的方向发展。     

Wearable Textile‐Based Co−Zn Alkaline Microbattery with High Energy Density and Excellent Reliability

Wearable in‐plane Zn‐based microbatteries are considered as promising micropower sources for wearable electronics due to their high capacity, low cost, high safety, and easy integration. However, their applications are severely impeded by inadequate energy density arising from unsatisfactory capacity of cathode and poor cycling stability caused by degradation of electrode materials and Zn dendrite. Additionally, the short‐circuit induced safety issue caused by Zn dendrite is still a roadblock for Zn‐based microbatteries. Herein, a textile‐based Co?Zn microbattery with ultrahigh energy density and excellent cycling stability is demonstrated. Benefiting from the fast electron transport of three‐dimensional (3D) porous Ni‐coated textile and synergistic effect from the hierarchical Co(OH)₂@NiCo layered double hydroxide (LDH) core?shell electrode, the fabricated Co?Zn microbattery with high flexibility delivers superior energy/power densities of 0.17 mWh cm^?2/14.4 mW cm^?2, outperforming most reported micro energy storage devices. Besides, the trench‐type configuration as well as the 3D porous Zn@carbon clothes can avoid the short‐circuit‐induced safety issues, resulting in excellent cycling stability (71% after 800 cycles). The unique core?shell structure and novel configuration provide a brand‐new design strategy for high‐performance wearable in‐plane microdevices.     

真空分级淬火对8Cr4Mo4V钢组织和性能的影响

在真空条件下对航空轴承用8Cr4Mo4V钢进行不同温度的分级淬火并采用扫描电镜观察其微观组织、用XRD谱进行相分析并测试洛氏硬度、冲击性能和旋转弯曲疲劳性能,研究了真空分级淬火对其微观组织和力学性能的影响。结果表明,真空分级淬火后的8Cr4Mo4V钢其微观组织由下贝氏体、马氏体/残余奥氏体和碳化物组成;随着分级淬火温度的提高,淬火和回火态钢中析出碳化物的数量增加,残余奥氏体的含量降低。分级淬火温度为580℃时淬火态钢中贝氏体的含量最高(达到13.87%),残余奥氏体的含量为28.59%。回火后析出碳化物的含量和洛氏硬度均为所有分级温度中的最大值,分别为4.37%和62.38HRC。真空分级淬火能提高8Cr4Mo4V钢的综合力学性能。与未分级真空淬火相比,进行580℃×10 min真空分级淬火的8Cr4Mo4V钢的冲击韧性提高了23.3%,旋转弯曲疲劳极限提高了110 MPa。     

Investigation of WC–Co alloy properties based on thermodynamic calculation and Weibull distribution

The influence of alloy composition and sintering temperature on the mechanical properties and reliability of WC–Co cemented carbides was studied theoretically and experimentally. For the first time, through a hybrid approach of thermodynamic calculations and Weibull distribution, the comprehensive performance of ultrafine WC–Co cemented carbides with different C contents and inhibitor type was investigated in detail. The carbon content of WC–10?wt-% Co–0.5?wt-% Cr cemented carbides was carefully controlled within the range of 5.38?5.52?wt-%. The contents of Cr and V are chosen to be in the range of 0–1?wt-%. It is found that WC–10?wt-% Co–0.5?wt-% Cr alloys with 5.46?wt-% C or 5.5?wt-% C show excellent mechanical properties and high reliability. WC–10?wt-% Co alloys with 0.5?wt-% Cr and 0.4?wt-% Cr–0.2?wt-% V demonstrate high mechanical property and reliability. The results of this study can be used to design process parameters during the manufacture of WC–Co cemented carbides.     

Study of Milling Time and Process Control Agent on W–Mo–Cr Pre-Alloying Powders

According to the experimental researches of dynamic friction polishing (DFP) technology, high density and hardness W–Mo–Cr alloy with strong graphitization ability of diamond can achieve a high material removal rate of diamond. In the preparation process of polishing plate, mechanical alloying (MA) method is used to synthetize pre-alloying powders by means of fierce mechanical action and supersaturated solid state reaction performed by high-energy ball milling. The effect and progress of MA are directly affected by the process parameters of ball milling. This article mainly summarizes the microstructural changes of W–Mo–Cr pre-alloying powders varying with milling time and process control agent (PCA) content, and their function mechanisms and potential causes are discussed. The reasonable process parameters of ball milling are optimized by single-factor experiments. The results show that under the conditions of 300 rpm rotation speed, 60 h milling time, and 10% PCA content, the surface activities, compositional uniformity, and grain refinement level of powders are heightened. The preparation of excellent pre-alloying powders provides early technical guarantee for the study of high density tungsten-based alloy used for DFP diamond.     

Measurement of an Iso‐Curie Temperature Line of a Co?Cr?Mo Solid Solution by Magnetic Force Microscopy Imaging on a Diffusion Multiple

The 24 °C iso‐Curie temperature line of a Co? Cr? Mo fcc solid solution is obtained by performing magnetic force microscopy (MFM) imaging on solid solution compositions created in a diffusion multiple. The MFM imaging clearly reveals the boundary that separates the paramagnetic region without magnetic domains from the ferromagnetic region with domains. Compositional analysis along the boundary yields a constant Curie temperature (24 °C) composition line. Such a measurement is more efficient than one‐alloy‐at‐a‐time tests and can be used to screen new ferromagnetic materials.     

Improving cytocompatibility of Co28Cr6Mo by TiO2 coating: gene expression study in human endothelial cells

Cobalt-based materials are widely used for coronary stents, as well as bone and joint implants. However, their use is associated with high corrosion incidence. Titanium alloys, by contrast, are more biocompatible owing to the formation of a relatively inactive titanium oxide (TiO₂) layer on their surface. This study was aimed at improving Co28Cr6Mo alloy cytocompatibility via sol–gel TiO₂ coating to reduce metal corrosion and metal ion release. Owing to their role in inflammation and tissue remodelling around an implant, endothelial cells present a suitable in vitro model for testing the biological response to metallic materials. Primary human endothelial cells seeded on Co28Cr6Mo showed a stress phenotype with numerous F-actin fibres absent on TiO₂-coated material. To investigate this effect at the gene expression level, cDNA microarray analysis of in total 1301 genes was performed. Compared with control cells, 247 genes were expressed differentially in the cells grown on Co28Cr6Mo, among them genes involved in proliferation, oxidative stress response and inflammation. TiO₂ coating reduced the effects of Co28Cr6Mo on gene expression in endothelial cells, with only 34 genes being differentially expressed. Quantitative real-time polymerase chain reaction and protein analysis confirmed microarray data for selected genes. The effect of TiO₂ coating can be, in part, attributed to the reduced release of Co²⁺, because addition of CoCl₂ resulted in similar cellular responses. TiO₂ coating of cobalt-based materials, therefore, could be used in the production of cobalt-based devices for cardiovascular and skeletal applications to reduce the adverse effects of metal corrosion products and to improve the response of endothelial and other cell types.     

Effect of quenching on microstructure and wear‐resistance of Fe–10Cr–1.5B–2Al Alloy

Cast Fe–10Cr–1.5B–2Al alloy was quenched at different temperatures. The effects of quenching temperature on microstructure and hardness and wear‐resistance of Fe–10Cr–1.5B–2.0Al alloy were investigated by means of the optical microscopy, the scanning electron microscope, X‐ray diffraction, energy dispersive spectrometer, Vickers hardness and Rockwell hardness tester, and the MM‐200 block‐on‐ring wear testing machine under dry friction condition. The results indicate that the as‐cast microstructure of Fe–10Cr–1.5B–2.0Al alloy consists of ferrite, pearlite and netlike eutectics which are distributed in the grain boundary. The eutectics mainly include herringbone M₂B and chrysanthemum M₇(C, B)₃. The matrix gradually turns into single martensite with the increase of the quenching temperature. The type of borocarbides has no obvious change after quenching. The netlike boride almost totally fractures and transforms from the fish‐bone structure to the graininess. There is some retained austenite in the quenched structures when the quenching temperature is more than 1100 °C. When the quenching temperature is in a range of 1000 °C to 1100 °C, the hardness and wear resistance show a sharp increase with an increase of temperature, and show a slight decrease after surpassing 1100 °C.     

Ni—20Cr—10Mo—10Co高温合金的相分析

Ni-20Cr-10Mo-10Co高温合金是以碳化物为主要强化相的一种铸造高温合金,用X射线衍射与扫描电镜的背散射象及能谱分析确定了该合金的相组成,即基体为Ni-Mo-Cr-Co的固溶体,及（Cr,Mo,Co,Ni)(23C6和（Mo,Cr,Co,Ni)6C两种碳化物。