Frederick E. Wang

Bio: Frederick E. Wang is an academic researcher from Silver Spring Networks. The author has contributed to research in topics: Crystal twinning & Fullerene. The author has an hindex of 11, co-authored 26 publications receiving 1088 citations.

Crystal Structure and a Unique ``Martensitic'' Transition of TiNi

Abstract: Through single‐crystal x‐ray diffraction methods, the crystal structure of TiNi has been determined in the temperature range −70° to 900°C. Contrary to what has been assumed from previous work based on the powder pattern methods, the TiNi crystal structure is not a simple CsCl type. Rather, it has an a0=9A superlattice and an a0=3A sublattice with 54 atoms per unit cell complex structure.The 9A superlattice undergoes, at about 166°C, a ``martensitic'' pseudo order‐disorder transition which is not accompanied by a crystallographic transformation. Through the understanding of this unique transition the apparent contradicting observations made on TiNi by various past investigators can now be reconciled and the unusual physical properties associated with the alloy are explained qualitatively.

The Irreversible Critical Range in the TiNi Transition

Abstract: Through an investigation of the transport and related thermodynamic properties of TiNi at and around its ``martensitic'' transition temperature, the existence of a critical range extending over a 60°C interval is established. Within this critical range, the phase transition is second order. Irreversibility of various properties within the critical range is interpreted in terms of irreversible shear movement of atoms. On the basis of transport data, the band structure of TiNi is inferred to be a single or ``nearly'' single positive band within the temperature range investigated. The postulate that some of the valence electrons undergo a ``covalent''→``conduction'' electronic transformation in the course of the second‐order transition is consistent in large measure with experimental data.

Mechanism of the TiNi Martensitic Transformation and the Crystal Structures of TiNi‐II and TiNi‐III Phases

Abstract: Based on combined x‐ray and neutron‐diffraction data, an inference for the coexistence of the B2(CsCl) and P3m1 structures in the TiNi‐II phase is made. Other experimental evidence indicates the proportion of the B2 to P3m1 structures to depend critically on the thermal and mechanical history of the alloy. Through a mechanism of an inhomogeneous‐but‐cooperative atomic shear in the 〈111〉B2 direction and a factor sequence, −(0−1−1)n− in the (110)B2 plane, the B2 and P3m1 structures transform into P1 abd P6/m structures, respectively, during the TiNi‐II to TiNi‐III martensitic transformation. Subsequent submicrotwinning at atomic level of the P1 structure leads to the P1 structure. Therefore, the TiNi‐III (``martensite'') phase may consist of the P1, P1, and P6/m structures.

Method of treating variable transition temperature alloys

Abstract: METAL ALLOYS OF THE FORMULA TINIXCO1-X, TICOXFE1-X, WHEREIN X IS AN INTEGER FROM 0 TO 1 UNDERGO MARTENSITIC TRANSITIONS OVER A VERY WIDE TEMPERATURE RANGE FROM LESS THAN 4*K. TO 1000*K. THE METAL ALLOYS ARE WORKED AND HEAT TREATED TO EFFECT A REVERSION BACK TO AN ORIGINAL CONFIGURATION AS THE RESULT OF THE MARTENSITIC TRANSITION OF THE ALLOYS DUE TO THE HEAT TREATMENT.

Medical devices incorporating SIM alloy elements

Abstract: Medical devices which are currently proposed to use elements made from shape memory alloys may be improved by the use of stress-induced martensite alloy elements instead. The use of stress-induced martensite decreases the temperature sensitivity of the devices, thereby making them easier to install and/or remove.

Metallic implant biomaterials

Abstract: Human tissue is structured mainly of self-assembled polymers (proteins) and ceramics (bone minerals), with metals present as trace elements with molecular scale functions. However, metals and their alloys have played a predominant role as structural biomaterials in reconstructive surgery, especially orthopedics, with more recent uses in non-osseous tissues, such as blood vessels. With the successful routine use of a large variety of metal implants clinically, issues associated with long-term maintenance of implant integrity have also emerged. This review focuses on metallic implant biomaterials, identifying and discussing critical issues in their clinical applications, including the systemic toxicity of released metal ions due to corrosion, fatigue failure of structural components due to repeated loading, and wearing of joint replacements due to movement. This is followed by detailed reviews on specific metallic biomaterials made from stainless steels, alloys of cobalt, titanium and magnesium, as well as shape memory alloys of nickel–titanium, silver, tantalum and zirconium. For each, the properties that affect biocompatibility and mechanical integrity (especially corrosion fatigue) are discussed in detail. Finally, the most critical challenges for metallic implant biomaterials are summarized, with emphasis on the most promising approaches and strategies.

Biomaterials in orthopaedics.

Abstract: At present, strong requirements in orthopaedics are still to be met, both in bone and joint substitution and in the repair and regeneration of bone defects. In this framework, tremendous advances in the biomaterials field have been made in the last 50 years where materials intended for biomedical purposes have evolved through three different generations, namely first generation (bioinert materials), second generation (bioactive and biodegradable materials) and third generation (materials designed to stimulate specific responses at the molecular level). In this review, the evolution of different metals, ceramics and polymers most commonly used in orthopaedic applications is discussed, as well as the different approaches used to fulfil the challenges faced by this medical field.