Laser heat treatment of titanium GRADE 1 with iron‐nickel powder

Titanium alloys thanks to their low density and high mechanical properties are a group of materials that are being used willingly nowadays. A promising method of titanium heat treatment is laser alloying. Process parameters like laser beam power, its traverse speed, amount of alloying elements and shield gas, have influence on the resulting material. Different chemical composition and morphology can be achieved resulting in a change of properties on the surface of the material. The paper presents the investigation of titanium GRADE 1 processed with iron‐nickel powder using laser alloying. The treatment was performed using a high power diode laser. Different laser beam power values were used. Treatment resulted in obtaining good‐adhere, porous‐free, uniform composite material with no cracks. Formation of new phases and solid solution was the reason why it was possible to achieve an increase in microhardness on the surface. Light microscopy, scanning electron microscopy with energy dispersive X‐ray spectroscopy examination, microhardness results and X‐ray diffraction are presented within the paper.     

Microstructure,biodegradation, antibacterial and mechanical properties of ZK60-Cu alloys prepared by selective laser melting technique

Magnesium (Mg) alloys are receiving increasing attention for body implants owing to their good biocompatibility and biodegradability. However, they often suffer from bacterial infections on account of their insufficient antibacterial ability. In this study, ZK60-xCu (x?=?0, 0.2, 0.4, 0.6 and 0.8?wt%) alloys were prepared by selective laser melting (SLM) with alloying copper (Cu) to enhance their antibacterial ability. Results showed that ZK60-Cu alloys exhibited strong antibacterial ability due to combination of release of Cu ions and alkaline environment which could kill bacteria by destroying cellular membrane structure, denaturing enzymes and inhibiting deoxyribonucleic acid (DNA) replication. In addition, their compressive strength increased due to grain refinement and uniformly dispersing of short-bar shaped MgZnCu phases. Moreover, ZK60-Cu alloys also exhibited good cytocompatibility. In summary, ZK60-Cu alloys with antibacterial ability may be promising implants for biomedical applications.     

Additive manufacturing of high entropy alloys:A practical review

The novel idea of alloying,which is based on the utilization of multiple principal elements in high concen-trations,has created a novel class of promising materials called high entropy alloys(HEAs).So far,several HEAs with outstanding properties beyond those of conventional alloys have been discovered,and new superior high-entropy alloys are still expected to be developed in the future.However,the fabrication process of HEAs through conventional manufacturing techniques suffers from significant limitations due to the intrinsic requirements of HEAs.Additive manufacturing(AM),on the other hand,has provided new opportunities for fabricating geometrically complex HEAs with the possibility of in situ tailoring of their microstructure features.Considering the growing interest in AM of HEAs during most recent years,this review article aims at providing the state of the art in AM of HEAs.It describes the feedstock requirements for laser based AM techniques.Thereafter,a comprehensive picture of the current state of nearly all HEAs processed by laser metal deposition(LMD),selective laser melting(SLM)and selec-tive electron beam melting(SEBM)is presented.Special attention is paid to the features of AM derived microstructures along with their outstanding properties and underlying mechanisms for various mate-rial processing combinations.The AM of interstitial solute hardening HEAs,HEA matrix composites as well as non-beam based AM of HEAs will also be addressed.The post-AM treatments and the strategies to fabricate defect-free HEAs are summarized.Finally,a conclusion of current state and future prospects of additive manufacturing of HEAs will be presented.     

Design and characterizations of novel biodegradable ternary Zn-based alloys with IIA nutrient alloying elements Mg,Ca and Sr

Apart from the industrial and automotive applications, Zn and Zn-based alloys are considered as a new kind of potential biodegradable material quite recently. However, one drawback of pure Zn as potential biodegradable metal lies in that pure Zn has quite low strength and plasticity. In the present study, three important IIA essential nutrient elements Mg, Ca and Sr and hot-rolling and hot-extrusion thermal deformations have been applied to overcome the drawback of pure Zn and benefit the biocompatibility of Zn-based potential implants. The microstructure, mechanical properties, corrosion behavior, hemocompatibility, in vitro cytocompatibility were studied systematically to investigate their feasibility as bioabsorbable implants. The results showed that the mechanical properties of the ternary Zn–1Mg–1Ca, Zn–1Mg–1Sr and Zn–1Ca–1Sr alloys are much higher than that of pure Zn, owing to both the alloying effects and thermal deformation effects. In vitro hemolytic rate test and cell viability test indicated that the addition of the IIA nutrient alloying elements Mg, Ca and Sr into Zn can benefit their hemocompatibility and cytocompatibility, which would further guarantee the biosafety of these new kind of biodegradable Zn-based implants for future clinical applications.     

Challenges and Solutions for the Additive Manufacturing of Biodegradable Magnesium Implants

Due to their capability of fabricating geometrically complex structures, additive manufacturing (AM) techniques have provided unprecedented opportunities to produce biodegradable metallic implants—especially using Mg alloys, which exhibit appropriate mechanical properties and outstanding biocompatibility. However, many challenges hinder the fabrication of AM-processed biodegradable Mg-based implants, such as the difficulty of Mg powder preparation, powder splash, and crack formation during the AM process. In the present work, the challenges of AM-processed Mg components are analyzed and solutions to these challenges are proposed. A novel Mg-based alloy (Mg–Nd–Zn–Zr alloy, JDBM) powder with a smooth surface and good roundness was first synthesized successfully, and the AM parameters for Mg-based alloys were optimized. Based on the optimized parameters, porous JDBM scaffolds with three different architectures (biomimetic, diamond, and gyroid) were then fabricated by selective laser melting (SLM), and their mechanical properties and degradation behavior were evaluated. Finally, the gyroid scaffolds with the best performance were selected for dicalcium phosphate dihydrate (DCPD) coating treatment, which greatly suppressed the degradation rate and increased the cytocompatibility, indicating a promising prospect for clinical application as bone tissue engineering scaffolds.     

Degradable silver-based alloys

Noble metals solved in iron implants are effective cathodes, which can suit to accelerate the corrosion rate of the base material. In terms of its antibacterial behavior as well as lower costs in comparison with gold or platinum, silver seems to be an attractive candidate to adapt the corrosion rate of implants to the medical requirements. However, the degradation of silver in human bodies is a time-consuming process, and is controversially discussed due to the unknown long-term effect of silver on the human organism. Alloying silver with chemical elements less resistant to corrosion in aqueous mediums, particularly, in simulated body fluid, can improve the degradability of silver. Therefore, the current study addresses the design of adapted silver alloys exhibiting improved degradability in comparison with pure silver. Pure silver and binary silver alloys containing silicon, magnesium and calcium are studied in terms of their microstructure, open-circuit potential and degradation rate.     

A high strength,wear and corrosion-resistant,antibacterial and biocompatible Nb-5 at.％ Ag alloy for dental and orthopedic implants

Refractory metal niobium (Nb) incorporated with a small amount of silver (Ag),the resulting Nb-Ag two-phase alloys,were fabricated by mechanical alloying and spark plasma sintering.The microstructure,mechanical properties,wear resistance,corrosion behavior,in vitro and in vivo antibacterial properties and biocompatibility of the Nb-Ag alloys were systematically investigated.The results show that the mechanical properties,wear resistance,corrosion resistance and antibacterial ability were significantly enhanced after addition of 5 at.％ Ag.The fabricated Nb-5 at.％ Ag alloy demonstrates high yield strength of up to ～ 1486 MPa and fracture strain of ～ 35 ％.The precipitated Ag particles could reduce friction and wear.The enhanced corrosion resistance was attributed to the higher relative density of the sintered alloys and the formation of a stable and dense passive film of niobium and silver oxides.In vitro and in vivo evaluations show that the Nb-5 at.％ Ag alloy also has strong antibacterial activity and good biocompati-bility and osteointegration ability.These results demonstrate great potential of the nanostructured Nb-Ag alloys for dental and orthopedic implants.     

生物医用多孔钛及钛合金激光快速成形研究进展

多孔钛及钛合金具有良好的生物相容性和与人骨更匹配的力学性能,是人体理想的替代材料,因此其制备技术及相关性能研究引起了广泛关注。激光快速成形是一项先进的制造技术,在制备生物多孔金属材料时具有独特的优势。介绍了激光快速成形的工作原理和技术特征,根据成形工艺特点简要回顾了4种代表性激光快速成形技术(选择性激光烧结、选择性激光熔化、激光近净成形和激光立体成形)的国内外发展现状,并重点论述了这几种技术在制备生物医用多孔钛及钛合金方面的最新研究进展,最后指出了今后在该领域的主要研究工作。     

Surface treatments for controlling corrosion rate of biodegradable Mg and Mg-based alloy implants

Due to their excellent biodegradability characteristics, Mg and Mg-based alloys have become an emerging material in biomedical implants, notably for repair of bone as well as coronary arterial stents. However, the main problem with Mg-based alloys is their rapid corrosion in aggressive environments such as human bodily fluids. Previously, many approaches such as control of alloying materials, composition and surface treatments, have been attempted to regulate the corrosion rate. This article presents a comprehensive review of recent research focusing on surface treatment techniques utilised to control the corrosion rate and surface integrity of Mg-based alloys in both in vitro and in vivo environments. Surface treatments generally involve the controlled deposition of thin film coatings using various coating processes, and mechanical surfacing such as machining, deep rolling or low plasticity burnishing. The aim is to either make a protective thin layer of a material or to change the micro-structure and mechanical properties at the surface and sub-surface levels, which will prevent rapid corrosion and thus delay the degradation of the alloys. We have organised the review of past works on coatings by categorising the coatings into two classes—conversion and deposition coatings—while works on mechanical treatments are reviewed based on the tool-based processes which affect the sub-surface microstructure and mechanical properties of the material. Various types of coatings and their processing techniques under two classes of coating and mechanical treatment approaches have been analysed and discussed to investigate their impact on the corrosion performance, biomechanical integrity, biocompatibility and cell viability. Potential challenges and future directions in designing and developing the improved biodegradable Mg/Mg-based alloy implants were addressed and discussed. The literature reveals that no solutions are yet complete and hence new and innovative approaches are required to leverage the benefit of Mg-based alloys. Hybrid treatments combining innovative biomimetic coating and mechanical processing would be regarded as a potentially promising way to tackle the corrosion problem. Synergetic cutting-burnishing integrated with cryogenic cooling may be another encouraging approach in this regard. More studies focusing on rigorous testing, evaluation and characterisation are needed to assess the efficacy of the methods.     

Recent advances in biodegradation controls over Mg alloys for bone fracture management: A review

Magnesium (Mg) alloys possess comparable physical and mechanical properties to bone, making them an outstanding candidate of implant materials for bone fracture treatment. In addition to the excellent biocompatibility, and bioactivity, the engagement of Mg alloys is key for a number of biological functionalities in the human body. The unique biodegradation nature of Mg alloy implants implies that it may not require a secondary removal procedure when the expected supporting tasks accomplish, as they may simply and safely “disappear” over time. Nonetheless, the demonstrated drawback of potentially rapid degradation, is an issue that must be addressed appropriately for Mg implants and is consequently given unique attention in this review article. Herein, the critical criteria and the state-of-the-art strategies for controlling the degradation process of Mg alloys are reported. Furthermore, future developments of biodegradable Mg and its alloys systems with satisfactory specifications for clinical trials and deployment, are discussed. This review aims to provide information to materials scientists and clinical practitioners in the context of developing practical biodegradable Mg alloys.     

Alloying of pure magnesium with Mg 33.3 wt-%Zr master alloy

Abstract

To capitalise on the strengthening potential of zirconium as a potent grain refiner for magnesium alloys, the mechanisms of adding zirconium to magnesium and its subsequent grain refining action need to be understood. Using a Mg- 33.3Zr master alloy (Zirmax supplied by Magnesium Elektron Ltd) as a zirconium alloying additive, the influence of different alloying conditions on the dissolution of zirconium in magnesium was investigated. It was found that owing to the highly alloyable microstructure of Zirmax, the dissolution of zirconium was generally complete within a few minutes in the temperature range 730 to 780°C. Prolonging and/or intensifying stirring were found to have no conspicuous influence on further enhancing the dissolution of zirconium. In all cases studied, the average grain size increased with increasing holding time at temperature while the total zirconium content decreased. The finest grain structure and highest total zirconium content corresponded to sampling immediately after stirring. Pick up of iron by molten magnesium from the mild steel crucibles used for melting and holding, was significantly delayed or avoided in the temperature range 730 to 780°C by coating the crucibles with boron nitride. It is therefore feasible to conduct zirconium alloying at 730°C without the need of a considerable excess of Zirmax addition using a properly coated or lined steel crucible.     

Surface electron beam melting and alloying of tool steels

Abstract

Surface melting and alloying of D3 steel using an electron beam has been carried out to improve its surface microstructure and properties. The solution of primary carbides, together with rapid solidification and subsequent cooling, enhance the solubility of alloying elements in the γ Fe phase and thus influence the behaviour of the steel on subsequent tempering. The surface melted zone consists of dendrites without primary carbides, which is also the case for samples alloyed with WC, SiC, or Al₂O₃. When alloyed with TiC or TiB₂, the materials contain TiC or TiB₂ primary phase respectively in addition to the iron rich dendrites. Some unmelted TiB₂ particles are also present. On tempering, both electron beam melting and alloying change the secondary hardening characteristics, increasing the peak hardness and the peak hardness temperature.

MST/1194     

激光熔覆TiCp／Ni基合金复合涂层中TiCp的行为

通过激光熔覆TiCp/Ni基合金复合涂层微观组织的研究表明,TiC颗粒在熔覆过程中表面发生部分溶解,当凝固时,溶解的部分TiC在残留TiC颗粒上重新外延生长析出,并与基体合金元素产生附加合金化,同时,TiC颗粒成为从激光熔体凝固各相优先形核的基底;TiC颗粒与凝固前沿间的相互作用控制其微观分布。     

生物医用可降解锌基合金的研究进展

锌基合金是近几年新兴的一种医用可降解材料,有望应用于心血管支架及骨植入等医疗器械。锌是人体必需的营养元素,具有良好的生物相容性及适宜的体内降解速率,作为可降解合金的基体有很广的应用前景。然而,生物可降解锌基合金的设计、加工、强化及降解机理等研究尚处于起步阶段,还需要做大量的基础研究工作。本文以最终医疗器械产品的理想标准要求为切入点,从生物相容性、力学性能及抗腐蚀性能等方面对近几年医用锌基合金的研究成果进行了综述分析,并展望了其未来的发展方向。     

Development and characterization of β-type Ti-Zr-Nb-Sn dental implant materials

To develop new materials of proper elastic modulus and biocompatibility for dental implants, Ti-2Zr-xNb-xSn (x = 0, 0.1, 0.2, 0.3) and Ti-2Zr-xNb-xMo (x = 0, 0.1, 0.2, 0.3) alloys were designed and fabricated. Effects of alloying elements on properties and the feasibility of application in dentistry are analyzed. It is indicated that Nb, Sn and Mo obviously influence the phase compositions of Ti-2Zr-based biological alloys. With the increase of alloying element content, all the alloys tend to form a single β-Ti phase. Ti-2Zr-xNb-xSn alloys exhibit better mechanical properties and corrosion resistance than the Ti-2Zr-xNb-xMo alloys. The Ti-2Zr-0.1Nb-0.1Sn alloy has proper elastic modulus (14.72 GPa) (which is very close to the natural bones), excellent corrosion resistance and comprehensive mechanical properties, and is considered as ideal candidate for implant materials.     

医用镁金属材料的研究进展

镁及其合金具有优良的综合力学性能、与人体良好的生物相容性能以及生物可降解吸收等特点,有望成为一类新型医用植入材料.综述了镁金属作为医用植入材料的研究发展现状,分析了其应用上的优势与不足,对医用镁金属的表面改性技术进行了简单的论述,并对其作为医用植入材料的发展前景进行了展望.     

Surface melting of cast iron with a high-power laser beam

Samples of cast iron were covered with an alloying material, Ti, Cr, Si, Vor Cb, and irradiated with a 2.5 kW laser beam. Partial melting of the sample surface was observed, and the alloying element dissolved. The carbide structure in the resolidified region was governed by the alloy addition. The effect of parameters such as beam diameter, scanning rate, power and alloy content have been investigated and the crack frequency evaluated.     

Novel Mg-based alloys by selective laser melting for biomedical applications: microstructure evolution,microhardness and in vitro degradation behaviour

Laser-melted Mg-3Zn-xDy (x?=?0, 1, 3, 5?wt. %) alloys were investigated as candidate materials for biodegradable metallic implant applications. The results showed that the α-Mg, MgZn₂ and Mg-Zn-Dy phases were distributed in the Dy-containing alloys. Due to the addition of Dy, the grain size was significantly refined. As the grain size decreased and the second phase content increased, the hardness monotonously increased. The degradation characteristics analysis via immersion testing indicated that the degradation rate of the laser-melted Mg-3Zn-1Dy alloys was remarkably reduced, evidenced by the corresponding lower average hydrogen evolution rate. Consequently, the Mg-3Zn-1Dy was considered to be a promising candidate for implant applications, due to the appropriate rate of mechanical integrity loss during degradation. Overall, the mitigated degradation rate was attributed to the refined grains, the homogeneous microstructure as well as a certain amount of second phase produced during the process of selective laser melting.     

合金化填充材料Ni 对SiCP/6061Al 复合材料激光焊接焊缝显微组织的影响

以N i 片作为合金化填充材料对SiC_P/6061A l 金属基复合材料(SiC_P/6061A lMMC) 进行激光焊接, 研究了激光输出功率、焊接速度等焊接工艺参数对焊缝显微组织的影响。结果表明, 采用金属N i 片作为合金化填充材料对SiC_P/6061A lMMC 进行激光焊接, 可以在一定程度上抑制SiC 颗粒的溶解及针状脆性相Al₄C₃ 的形成, 并获得以Al₃Ni 等相为增强相的焊缝显微组织, 但在焊缝心部有粗大的气孔形成。      

Phase investigation in laser surface alloyed steels with TiC

Laser technology enables melting and alloying specimen surfaces without the substrate itself being heated, whereby surfaces with special attributes are obtained with the properties of the substrate remaining unaffected. The surfaces of Armco iron and AISI 1045 steel were laser-alloyed with TiC powder, a CO₂ laser of 2.5 kW maximum power being used. Optimal laser and powder-feed parameters were established. Particles of TiC were injected into the molten surface layer, forming a composite material, steel + TiC. The microstructures were investigated metallographically. Some of the particles had partially melted during their passage through the laser beam and had re-solidified, forming small and fine dendrites. Phase identification by X-ray diffraction revealed the presence of -Fe, martensite, and Fe₃C phases, as well as amounts of stochiometric TiC and unknown phases. Identification of phases by TEM and diffraction of electrons revealed the presence of unknown phases, such as tetragonal TiC and (FeTi)C. Mössbauer results show ternary Fe-Ti-C phases, which can be related to the TEM and X-ray diffraction results. A correlation was found between the substrate's composition, microstructures, and the different phases present.