Metals

Corrosion destroys more than three percent of the world’s gross domestic product. Therefore, the design of highly corrosion-resistant materials is urgently needed. By breaking the classical alloy-design philosophy, high-entropy alloys (HEAs) possess unique microstructures, which are solid solutions with random arrangements of multiple elements. The particular locally-disordered chemical environment is expected to lead to unique corrosion-resistant properties. In this review, the studies of the corrosion-resistant HEAs during the last decade are summarized. The corrosion-resistant properties of HEAs in various aqueous environments and the corrosion behavior of HEA coatings are presented. The effects of environments, alloying elements, and processing methods on the corrosion resistance are analyzed in detail. Furthermore, the possible directions of future work regarding the corrosion behavior of HEAs are suggested.

Metals have been used for orthopedic implants for a long time due to their excellent mechanical properties. With the rapid development of additive manufacturing (AM) technology, studying customized implants with complex microstructures for patients has become a trend of various bone defect repair. A superior customized implant should have good biocompatibility and mechanical properties matching the defect bone. To meet the performance requirements of implants, this paper introduces the biomedical metallic materials currently applied to orthopedic implants from the design to manufacture, elaborates the structure design and surface modification of the orthopedic implant. By selecting the appropriate implant material and processing method, optimizing the implant structure and modifying the surface can ensure the performance requirements of the implant. Finally, this paper discusses the future development trend of the orthopedic implant.

Electron Beam Melting (EBM) is an Additive Manufacturing technique which can be used to fabricate complex structures from alloys such as Ti6Al4V, for example for orthopaedic applications. Here we describe the use of EBM for the fabrication of a novel Ti6Al4V structure of a regular diamond lattice incorporating graded porosity, achieved via changes in the strut cross section thickness. Scanning Electron Microscopy and micro computed tomography analysis confirmed that generally EBM reproduced the CAD design of the lattice well, although at smaller strut sizes the fabricated lattice produced thicker struts than the model. Mechanical characterisation of the lattice in uniaxial compression showed that its behaviour under compression along the direction of gradation can be predicted to good accuracy with a simple rule of mixtures approach, knowing the properties and the behaviour of its constituent layers.

Since Pourbaix presented Eh versus pH diagrams in his “Atlas of Electrochemical Equilibria in Aqueous Solution”, diagrams have become extremely popular and are now used in almost every scientific area related to aqueous chemistry. Due to advances in personal computers, such diagrams can now show effects not only of Eh and pH, but also of variables, including ligand(s), temperature and pressure. Examples from various fields are illustrated in this paper. Examples include geochemical formation, corrosion and passivation, precipitation and adsorption for water treatment and leaching and metal recovery for hydrometallurgy. Two basic methods were developed to construct an Eh-pH diagram concerning the ligand component(s). The first method calculates and draws a line between two adjacent species based on their given activities. The second method performs equilibrium calculations over an array of points (500 × 800 or higher are preferred), each representing one Eh and one pH value for the whole system, then combines areas of each dominant species for the diagram. These two methods may produce different diagrams. The fundamental theories, illustrated results, comparison and required conditions behind these two methods are presented and discussed in this paper. The Gibbs phase rule equation for an Eh-pH diagram was derived and verified from actual plots. Besides indicating the stability area of water, an Eh-pH diagram normally shows only half of an overall reaction. However, merging two or more related diagrams together reveals more clearly the possibility of the reactions involved. For instance, leaching of Au with cyanide followed by cementing Au with Zn (Merrill-Crowe process) can be illustrated by combining Au-CN and Zn-CN diagrams together. A second example of the galvanic conversion of chalcopyrite can be explained by merging S, Fe–S and Cu–Fe–S diagrams. The calculation of an Eh-pH diagram can be extended easily into another dimension, such as the concentration of a given ligand, temperature or showing the solubility of stable solids. A personal computer is capable of drawing the diagram by utilizing a 3D program, such as ParaView, or VisIt, or MATLAB. Two 3D wireframe volume plots of a Uranium-carbonate system from Garrels and Christ were used to verify the Eh-pH calculation and the presentation from ParaView. Although a two-dimensional drawing is still much clearer to read, a 3D graph can allow one to visualize an entire system by executing rotation, clipping, slicing and making a movie.

Kính kim loại khối dựa trên titan (Ti-based bulk metallic glasses - BMGs) rất hấp dẫn cho các ứng dụng do những đặc tính vượt trội của chúng như độ bền riêng cao và khả năng chống ăn mòn tốt. Trong bài báo này, chúng tôi sẽ tóm tắt tình hình hiện tại của nghiên cứu và phát triển kính kim loại khối dựa trên titan. Sự chú ý sẽ được đặt vào khả năng hình thành kính, các tính chất cơ học, khả năng chống ăn mòn và tương thích sinh học.

An insight of the dominant fracture mechanisms occurring in mechanical metallic components during industrial service conditions is offered through this short overview. Emphasis is given on the phenomenological aspects of fracture and their relationships with the emergent fracture mode(s) with respect to the prevailed operating parameters and loading conditions. This presentation is basically fulfilled by embracing and reviewing industrial case histories addressed from a technical expert viewpoint. The referenced case histories reflected mainly the author’s team expertise in failure analysis investigation. As a secondary perspective of the current study, selected failure investigation and prevention methodological approaches are briefly summarized and discussed, aiming to provide a holistic overview of the specific frameworks and systems in place, which could assist the organization of risk minimization and quality enhancement.

Hành vi ăn mòn và răng cưa của các hợp kim năng lượng cao TiZr0.5NbCr0.5, TiZr0.5NbCr0.5V và TiZr0.5NbCr0.5Mo trong dung dịch NaCl và H2SO4 đã được nghiên cứu thông qua các thí nghiệm phân cực động (PP) và thử nghiệm nhúng. Kết quả cho thấy tất cả các hợp kim đều thể hiện khả năng chống ăn mòn tuyệt vời, không phân biệt trong dung dịch NaCl hay trong dung dịch H2SO4. Việc bổ sung V và Mo làm tăng khả năng chống ăn mòn rỗ mặt cho cả ba hợp kim trong dung dịch NaCl một cách nhẹ nhàng và cải thiện mạnh mẽ khả năng chống ăn mòn trong dung dịch H2SO4. Hành vi ăn mòn của hợp kim TiZr0.5NbCr0.5 và TiZr0.5NbCr0.5Mo nhạy cảm hơn với nhiệt độ so với hợp kim TiZr0.5NbCr0.5V. Sau khi nhúng, bề mặt của hợp kim TiZr0.5NbCr0.5 xuất hiện một số lỗ rỗ, điều này có thể liên quan đến tiếng ồn điện hóa và hành vi răng cưa trên các đồ thị PP; sự ăn mòn cục bộ chủ yếu bắt đầu ở các ranh giới của pha Cr2Zr BCC và Laves đối với hợp kim TiZr0.5NbCr0.5V; trong khi đối với hợp kim TiZr0.5NbCr0.5Mo, các dendrites với vùng giàu nguyên tố Mo cho thấy khả năng chống ăn mòn kém.

The properties of carbides, such as morphology, size, and type, in H13 hot work die steel were studied with optical microscopy, transmission electron microscopy, electron diffraction, and energy dispersive X-ray analysis; their size distribution and quantity after tempering, at different positions within the ingot, were analyzed using Image-Pro Plus software. Thermodynamic calculations were also performed for these carbides. The microstructures near the ingot surface were homogeneous and had slender martensite laths. Two kinds of carbide precipitates have been detected in H13: (1) MC and M6C, generally smaller than 200 nm; and (2) M23C6, usually larger than 200 nm. MC and M6C play the key role in precipitation hardening. These are the most frequent carbides precipitating at the halfway point from the center of the ingot, and the least frequent at the surface. From the center of the ingot to its surface, the size and volume fraction of the carbides decrease, and the toughness improves, while the contribution of the carbides to the yield strength increases.

Hàn ảnh hưởng tốc độ cao là một loại quy trình hàn trạng thái rắn, là một trong những giải pháp để kết nối các vật liệu khác nhau mà không làm phát sinh các hợp kim giữa. Đến nay, đã có năm phương pháp chính được phát triển. Đó là hàn súng khí (GGW), hàn nổ (EXW), hàn xung từ trường (MPW), hàn tác nhân lá bay hơi (VFAW) và hàn tác động bằng laser (LIW). Tất cả đều có cơ chế hàn tương tự, nhưng chúng cũng có nguồn năng lượng và ứng dụng khác nhau. Bài đánh giá này chủ yếu tập trung vào nghiên cứu liên quan đến thiết lập thí nghiệm của các phương pháp hàn khác nhau, hiện tượng tia, đặc điểm giao diện hàn và các tham số hàn. Phần giới thiệu nêu bật tầm quan trọng của hàn ảnh hưởng tốc độ cao trong việc kết nối các vật liệu khác nhau. Bài đánh giá về các thiết lập thí nghiệm cung cấp tình hình hiện tại và các hạn chế của các quy trình hàn khác nhau. Hiện tượng tia, đặc điểm giao diện hàn và các tham số hàn đều liên quan đến cơ chế hàn. Kết luận và công việc trong tương lai được tóm tắt lại.

Ultrasonic Impact Treatment (UIT) is an effective technique for surface refinement and residual stress reduction, which is widely used in welding. This study investigates UIT-assisted Wire and Arc Additive manufacturing (WAAM). The residual stress, grain morphology and mechanical properties of post-UIT and as-deposited samples are studied. The result demonstrates that the UIT has a significant influence on the decrease of the residual stress. Moreover, the residual stress of the post-UIT samples is much lower than that of the as-deposited samples. The samples fabricated by UIT-assisted WAAM have a novel, bamboo-like distribution of prior-β grains, an alternating distribution of short columnar grains and equiaxed grains. The grain size of this bamboo-like structure is much smaller than the coarsen columnar grains. In addition, the mechanical properties of the post-UIT and as-deposited samples are compared. The results indicate that the average tensile strength of the post-UIT samples is higher, while the average elongation of the post-UIT samples is lower.