0411ctt fracture lo res

[Image above] Credit: Nicole Quevillon; Flickr CC BY-NC 2.0

[Editor’s note] This report comes to us from ACerS Fellow Jose S. Moya (jsmoya@icmm.csic.es) and José F. Bartolomé (jbartolo@icmm.csic.es), both affiliated with the Instituto de Ciencia de Materiales de Madrid (ICMM) in Spain.


Researchers at the Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC) in Spain have developed a new zirconium dioxide–tantalum (ZrO2–Ta) ceramic–metal composite, or biocermet, with an unprecedented combination of high toughness, strength, damage tolerance, and fatigue resistance.

Biocermets are promising candidate materials for designing damage tolerant components for aerospace applications, cutting and drilling tools, biomedical implants, and more.

By controlling the material’s microstructure at different scales, the ICMM-CSIC team discovered that the zirconium dioxide–tantalum biocermet has impressive elastic and plastic properties (yield stress and elastic modulus).

Properties such as damage tolerance (toughness) and fatigue resistance are generally mutually exclusive. Therefore, fail safe or damage tolerant design requires fatigue analysis and fatigue strength predictions for components in biomedical implants, spacecraft and rocket engines, cutting and drilling tools, fuselage of supersonic airplanes,  and more.

The ICMM-CSIC group developed a biocermet that overcame these difficulties by starting with a zirconia reinforced with 20 vol.% of uniformly distributed niobium flakes, produced by attrition milling of commercial metal powders.

Synergistic toughening mechanisms promote interactions between transformation toughening and crack bridging in these composites, resulting in fracture and damage resistance properties that have never been achieved with oxide ceramics. However, the materials showed low fatigue resistance under cyclic loading.

Next, the team reinforced a zirconia matrix with lamellar tantalum flakes. Interrelations between different strengthening and toughening mechanisms made it difficult for cracks to propagate, improving the material’s toughness to 16 MPa·m1/2. Commercial ceramic materials, such as alumina, yttria-stabilized zirconia, and alumina-zirconia composites, have flexural strengths of up to ~1.5 GPa.

This new material displays the highest combination of fracture toughness and strength ever reported for a biocompatible ceramic and requires increasing stress intensity to propagate cracks. Therefore, this biocermet compares favorably to commercial fine-grain alumina or zirconia ceramics.

In addition, it has far superior resistance to cyclic fatigue (measured in terms of fatigue life and fatigue limit) and damage tolerance fatigue compared to zirconium dioxide–niobium biocermets.

In the case of zirconium dioxide–tantalum composites, conflicts between mutually exclusive properties of toughness and fatigue resistance can be avoided through the presence of multiple mechanisms acting at different length scales, decreasing local stresses through limited plastic deformation. This provides intrinsic toughness and further extrinsic mechanisms, such as elastic bridging of tantalum particles, with about double the elastic modulus and yield strength values as niobium particles.

These unprecedented properties could stimulate multidisciplinary applied research on zirconium dioxide–tantalum composites, which are attractive for various fields, such as thermoelectric power generation, functionally graded materials, biomaterials, strain-tolerant and thermal-shock-resistant multifunctional ceramics, static-charge dissipation devices, and electric-discharge manufacturing. These developments could open the doors for massive and sustainable utilization of cyclic fatigue resistance structures.

The open-access paper, published in Scientific Reports, is “Unprecedented simultaneous enhancement in damage tolerance and fatigue resistance of zirconia/Ta composites” (DOI:10.1038/srep44922).