R.H.J. Hannink

Bio: R.H.J. Hannink is an academic researcher from Commonwealth Scientific and Industrial Research Organisation. The author has contributed to research in topics: Cubic zirconia & Ceramic. The author has an hindex of 12, co-authored 35 publications receiving 2053 citations. Previous affiliations of R.H.J. Hannink include Australian Nuclear Science and Technology Organisation.

Transformation Toughening in Zirconia‐Containing Ceramics

Abstract: The recognition of the potential for enhanced fracture toughness that can be derived from controlled, stress-activated tetragonal (t) to monoclinic (m) transformation in ZrO2-based ceramics ushered in a new era in the development of the mechanical properties of engineering ceramics and provided a major impetus for broader-ranging research into the toughening mechanisms available to enhance the fracture properties of brittle-matrix materials. ZrO2-based systems have remained a major focal point for research as developments in understanding of the crystallography of the t→m transformation have led to more-complete descriptions of the origins of transformation toughening and definition of the features required of a transformation-toughening system. In parallel, there have been significant advances in the design and control of microstructure required to optimize mechanical properties in materials developed commercially. This review concentrates on the science of the t→m transformation in ZrO2 and its application in the modeling of transformation-toughening behavior, while also summarizing the microstructural control needed to use the benefits in ZrO2-toughened ceramics.

Metastability of the Martensitic Transformation in a 12 mol% Ceria‐Zirconia Alloy: II, Grinding Studies

Abstract: Observations of the grinding-induced transformation in singlephase Ce-TZP materials, referred to in an earlier paper, are presented. Two techniques were used to grind the surface: by hand in a slurry of abrasive particles and with a high-speed diamond-impregnated wheel. Significant differences in X-ray diffraction profiles between the two grinding methods was observed. Limited monoclinic ZrO2 was detected on the machineground surface, along with the reversal of the tetragonal ZrO2 (200) peak intensities. On the hand-ground surface, considerable monoclinic phase was observed. The disappearance of the monoclinic phase with heating was followed by X-ray diffraction, and the Af was found to exceed 700°C, while the reversal in tetragonal (200) peak symmetry and intensity remained unaltered up to at least 1000°C. Transmission electron microscope studies at various depths below the ground surface were undertaken to identify the differences between these surfaces and fractured surfaces. A simple explanation is proposed for the reversal of the tetragonal peak intensities. This reversal has previously led to the notion of a ferroelastic toughening mechanism in similar TZP materials.

Progress in Transformation Toughening of Ceramics

Abstract: Historically, pure zirconia has been of limited use as a structural ceramic because of its polymorphic tetragonal to monoclinic (t -+ m) phase trans­ formation at about 1200°C, which causes catastrophic fracture behavior, i.e. structural unreliability (1). However, other physical and chemical fea­ tures make zirconia ceramics highly attractive for a large number of appli­ cations. These features include hardness, wear-resistance, high elastic modulus, chemical inertness, ionic and electrical properties, creep-resist­ ance, poor thermal conductivity, and high melting temperatures. Because of these physical attributes, and the more important aspect of what has become known as transformation toughening, much effort has been expended in understanding the phenomena and the associated thermo­ mechanical and chemical property behavior of zirconia-toughening systems (2-7). Transformation toughening (TT) now forms part of a class of toughen­ ing mechanisms that can be invoked to improve the fracture behavior of ceramics (8, 9). The family of toughening mechanisms is referred to as crack-tip shielding, which operate by reduction of the applied stress at the

Relationship between Fracture. Toughness and Phase Assemblage in Mg-PSZ

Abstract: The phase content, size, and distribution have a marked effect on the thermomechanical properties of a 9 mol% MgO-ZrO[sub 2] (Mg-PSZ) alloy. The work undertaken in this study is the first investigation the simultaneously measure and characterize the quantitative bulk phase contents and correlate these parameters to the fracture toughness and R-curve behavior of a variously aged Mg-PSZ alloy. Quantitative bulk phase characterization entailed a systematic evaluation using neutron diffraction. In addition, microscopy techniques were used to determine the phase distribution and assemblage. The results indicate that the maximum toughness is attained, for a constant tetragonal precipitate size, when the anion-ordered [delta]-phase (Mg[sub 2]Zr[sub 5]O[sub 12]) replaces a major portion of the cubic matrix phase after an 1,100 C aging treatment. The shape of the R-curve and the stress required to transform the tetragonal precipitates are also significantly influenced by the [delta]-phase content.

Influence of Thermal Decomposition on the Mechanical Properties of Magnesia-Stabilized Cubic Zirconia

Abstract: Cubic magnesia-stabilized zirconia was decomposed by isothermal heat treatment at 1100°C. The mechanical properties, including strength, fracture toughness, and hardness, were measured at various stages during the decomposition process. The strength initially decreased with aging but then recovered almost to its initial value. This strength decrease was associated with cracking of islands of the cubic phase in the matrix of monoclinic zirconia. The fracture toughness followed the strength although it was found that the monoclinic phase exhibited stable crack growth during notched beam fracture experiments or R-curve behavior. Measurements of the hardness indicated that the cubic phase was much harder than the monoclinic phase. In addition, X-ray diffraction, optical, and transmission electron microscopy studies were made of the decomposition process.

Transformation Toughening in Zirconia‐Containing Ceramics

Abstract: The recognition of the potential for enhanced fracture toughness that can be derived from controlled, stress-activated tetragonal (t) to monoclinic (m) transformation in ZrO2-based ceramics ushered in a new era in the development of the mechanical properties of engineering ceramics and provided a major impetus for broader-ranging research into the toughening mechanisms available to enhance the fracture properties of brittle-matrix materials. ZrO2-based systems have remained a major focal point for research as developments in understanding of the crystallography of the t→m transformation have led to more-complete descriptions of the origins of transformation toughening and definition of the features required of a transformation-toughening system. In parallel, there have been significant advances in the design and control of microstructure required to optimize mechanical properties in materials developed commercially. This review concentrates on the science of the t→m transformation in ZrO2 and its application in the modeling of transformation-toughening behavior, while also summarizing the microstructural control needed to use the benefits in ZrO2-toughened ceramics.

Material fundamentals and clinical performance of plasma-sprayed hydroxyapatite coatings: A review

Abstract: The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has aroused as many controversies as interests over the last decade. Although faster and stronger fixation and more bone growth have been revealed, the performance of HA-coated implants has been doubted. This article will initially address the fundamentals of the material selection, design, and processing of the HA coating and show how the coating microstructure and properties can be a good predictor of the expected behavior in the body. Further discussion will clarify the major concerns with the clinical use of HA coatings and introduce a comprehensive review concerning the outcomes experienced with respect to clinical practice over the past 5 years. A reflection on the results indicates that HA coatings can promote earlier and stronger fixation but exhibit a durability that can be related to the coating quality. Specific relationships between coating quality and clinical performance are being established as characterization methods disclose more information about the coating.

Understanding Degradation Mechanisms and Improving Stability of Perovskite Photovoltaics.

Abstract: This review article examines the current state of understanding in how metal halide perovskite solar cells can degrade when exposed to moisture, oxygen, heat, light, mechanical stress, and reverse bias. It also highlights strategies for improving stability, such as tuning the composition of the perovskite, introducing hydrophobic coatings, replacing metal electrodes with carbon or transparent conducting oxides, and packaging. The article concludes with recommendations on how accelerated testing should be performed to rapidly develop solar cells that are both extraordinarily efficient and stable.