There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The mechanical behavior, and thus ‘trustworthiness’/durability, of engineering components fabricated via laser-based additive manufacturing (LBAM) is still not well understood. This is adversely affecting the continual adoption of LBAM for part fabrication/repair within the global industry at large. Hence, it is important to determine the mechanical properties of parts fabricated via LBAM as to predict their performance while in service. This article is part of two-part series that provides an overview of Direct Laser Deposition (DLD) for additive manufacturing (AM) of functional parts. The first part (Part I) provides a general overview of the thermo-fluid physics inherent to the DLD process. The objective of this current article (Part II) is to provide an overview of the mechanical characteristics and behavior of metallic parts fabricated via DLD, while also discussing methods to optimize and control the DLD process. Topics to be discussed include part microstructure, tensile properties, fatigue behavior and residual stress – specifically with their relation to DLD and post-DLD process parameters (e.g. heat treatment, machining). Methods for controlling/optimizing the DLD process for targeted part design will be discussed – with an emphasis on monitored part temperature and/or melt pool morphology. Some future challenges for advancing the knowledge in AM-part adoption are discussed. Despite various research efforts into DLD characteristics and process optimization, it is clear that there are still many areas that require further investigation.

An overview of Direct Laser Deposition for additive manufacturing; Part II: Mechanical behavior, process parameter optimization and control

Ecological trends in machining as a key factor in sustainable production – A review

THE only addition to this issue of “Steel and its Heat Treatment” is a chapter on nitriding, contributed by Dr. V. O. Homerberg. In the space of sixteen pages a brief outline is given of the nature and conduct of the nitriding process, of the steels suitable for nitriding, and of their properties after treatment. Otherwise the book remains the same, although eight years have passed since the preparation of the previous edition. There is still, therefore, no reference to the notched-bar impact tests to which British metallurgists rightly attach so much importance, to grain size control (although this originated in America), to the newer types of stainless steels, or to manganese -molybdenum steels.Steel and its Heat TreatmentD. K.BullensBy. Third edition, rewritten and reset. Pp. xiii + 580. (New York: John Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1935.) 25s. net.

Steel and its heat treatment

Hydrogels have been developed since the 1960s for applications in personal care, medicine, and engineering. Evidence has accumulated that hydrogels under prolonged loads suffer fatigue. Symptoms include change in properties, as well as nucleation and growth of cracks. This article is the first review on the fatigue of hydrogels. Emphasis is placed on the chemistry of fatigue—concepts and experiments that link symptoms of fatigue to processes of molecules. Symptoms of fatigue are characterized by testing samples with and without precut cracks, subject to prolonged static and cyclic loads. We describe the use of energy release rate for samples with precut cracks, under the conditions of large-scale inelasticity, for hydrogels of complex rheology. Highlighted are three experimental setups: pure shear, tear, and peel, where energy release rate is readily obtained for materials of arbitrary rheology. We describe chemistries of bonds and topologies of networks. Noncovalent bonds and some covalent bonds are reversible: they reform after breaking under relevant conditions. Most covalent bonds are irreversible. Each topology of networks is a way to connect reversible and irreversible bonds. We review experimental data of hydrogels of five representative topologies of networks. We compare the Lake-Thomas threshold, the cyclic-fatigue threshold, and the static-fatigue threshold. Fatigue is a molecular disease. All symptoms of fatigue originate from one fundamental cause: molecular units of a hydrogel change neighbors under prolonged loads. Fatigue correlates with rheology, according to which we distinguish poroelastic fatigue, viscoelastic fatigue, and elastic-plastic fatigue. Many hydrogels have sacrificial bonds that act as tougheners. We distinguish tougheners of two types according to their stress-relaxation behavior under a prolonged static stretch. A liquid-like toughener relaxes to zero stress, and increases neither static-fatigue threshold nor cyclic-fatigue threshold. A solid-like toughener relaxes to a nonzero stress, increases static-fatigue threshold, but does not increase cyclic-fatigue threshold. We outline a strategy to create hydrogels of high endurance. Because of the molecular diversity among hydrogels, the chemistry of fatigue holds the key to the discovery of hydrogels of properties previously unimagined. It is hoped that this review helps to connect chemists and mechanicians.

Fatigue of hydrogels

Hardening of Steels, L. de C.F. Canale and G.E. Totten Quenching of Aluminum Alloys, R.T. Shuey and M. Tiryakiogliu Quenching of Titanium Alloys, L. Meekisho, X. Yao, and G.E. Totten Mechanical Properties of Ferrous and Nonferrous Alloys after Quenching, H.-J. Spies Thermo- and Fluid-Dynamic Principles of Heat Transfer during Cooling, F. Mayinger Heat Transfer during Cooling of Heated Metals with Vaporizable Liquids, R. Jeschar, E. Specht, and C. Kohler Wetting Kinematics, H.M. Tensi Wetting Kinetics and Quench Severity of Selected Vegetable Oils for Heat Treatment, K.N. Prabhu Residual Stresses after Quenching, V. Schulze, O. Vohringer, and E. Macherauch Effect of Workpiece Surface Properties on Cooling Behavior, F. Moreaux, G. Beck, and P. Archambault Determination of Quenching Power of Various Fluids, H.M. Tensi and B. Liscic Types of Cooling Media and Their Properties, W. Luty Gas Quenching, G. Belinato, L. de C.F. Canale, and G.E. Totten Techniques of Quenching, H.E. Boyer, P. Archambault, and F. Moreaux Intensive Steel Quenching Methods, N.I. Kobasko Prediction of Hardness Profi le in Workpiece Based on Characteristic Cooling Parameters and Material Behavior during Cooling, H.M. Tensi and B. Liscic Simulation of Quenching, C. Simsir and C. Hakan Gur Appendices Index

Quenching theory and technology

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Failure Analysis of Heat Treated Steel Components

Corrosion processes due to contact with the physiological environment should be avoided or minimized in orthopedic implants. Four metallic substrates frequently used as biomaterials: pure Ti, Ti-6Al-4V alloy, ASTM F138 stainless steel, and Co-Cr-Mo alloy, were coated with TiN using the physical vapor deposition (PVD) technique. These coatings have been screened by polarization curves in physiological solutions. TiN prepared by PVD is efficient as coating for stainless steel. On titanium and alloy there are no benefits concerning the corrosion resistance compared to the bare Ti-materials. TiN coatings have been screened according to ISO 10993 standard tests for biocompatibility and exhibited no cytotoxicity, dermal irritation, or acute systemic toxicity response.

Metallic biomaterials TiN-coated: corrosion analysis and biocompatibility.

The influence of the amount of retained austenite on short fatigue crack growth and wear resistance in carburized SAE 8620 steel was studied in this article. Different amounts of retained austenite in the microstructure of the carburized case were obtained through different heat treatment routes applied after the carburizing process. The wear tests were carried out using pin on disk equipment. After every 200 turns the weight loss was registered. Four point bend fatigue tests were carried out at room temperature, using three different levels of stress and R = 0.1. Crack length versus number of cycles and crack growth rate versus mean crack length curves were analyzed. In both tests the results showed that the test pieces with higher levels of retained austenite in the carburized case exhibited longer fatigue life and better wear resistance.

Influence of retained austenite on short fatigue crack growth and wear resistance of case carburized steel

The results of the stress relieving and tempering processes are dependent on the temperature and time of the process, which may be correlated using a parameter such as Holloman's (Holloman-Jaffe) parameter or the Larsen-Miller parameter. These parameters are a measure of the thermal effect of the process on the metallurgical transformation of the steel during tempering. The processes that exhibit the same tempering parameter are expected to exhibit the same effect (such as hardness). However, these more traditional numerical expressions assume isothermal tempering processes which seldom exist in production tempering ovens due to the heat-up period prior to soaking

Lauralice de Campos Franceschini Canale

Papers

Quenching theory and technology

Failure Analysis of Heat Treated Steel Components

Metallic biomaterials TiN-coated: corrosion analysis and biocompatibility.

Influence of retained austenite on short fatigue crack growth and wear resistance of case carburized steel

A historical overview of steel tempering parameters