In Situ X-ray Synchrotron Radiation Analysis, Tensile- and Biodegradation Testing of Redox-Alloyed and Sintered MgCa-Alloy Parts Produced by Metal Injection Moulding

Martin Wolff,Heike Helmholz,Regine Willumeit-Römer,Monika Luczak,Thomas Ebel,Daniel Strerath

doi:10.3390/met12020353

Abstract

Binary MgCa alloys are one of the promising and well investigated biodegradable metals and therefore a good standard for the study of novel processing routes. In this investigation, novel powder metallurgical (PM) blending and sintering methods were applied for the generation of biodegradable MgCa test specimens, using metal injection moulding (MIM). In addition to the classical PM-blending route using Ca-containing master-alloys, Ca-containing ceramics and hydrides, as there are CaO and CaH2, were used separately and in a stoichiometric mixture. In situ X-ray synchrotron radiation experiments were performed for a deeper understanding of alloy forming mechanisms during sintering. Mechanical and degradation performance was investigated by tensile testing and the monitoring of biodegradation under physiological conditions. Besides its sound strength of up to 144 MPa and degradation rate of 0.25 mm/a, the new redox alloying technique avoids the usage of any greenhouse active SF6 gas (global warming potential 22,800) during alloying, keeping the earth’s atmosphere safer. Therefore, it can be concluded that Ca-containing ceramics and hybrids are attractive alternatives to obtain, comparable to Mg-based materials, thus enabling safer processing.

Highlights

The suitability of calcium (Ca) as an appropriate alloying element for biodegradableMg-alloys was well investigated within the last two decades [1,2,3,4,5,6]
The only difference between these four blended Mg-0.8Ca routes (_oxy, _hyd, _stoi, _ref) is how the way calcium was introduced into the alloy
The procedure of introducing the Ca into the alloy determined the differences in shrinkage behaviour and residual porosity of the samples produced by the four blended Mg-0.8Ca routes

Summary

Introduction

The suitability of calcium (Ca) as an appropriate alloying element for biodegradableMg-alloys was well investigated within the last two decades [1,2,3,4,5,6]. Since a couple of years ago, in addition to common casting and machining technologies, powder metallurgy approaches based on sintering have become available This allows processing by metal injection moulding (MIM) or additive manufacturing technologies, which are very attractive with regard to freedom in geometry as well as in costs. For biomedical applications, rather low amounts of alloys in terms of mass but high in the number of variations in composition are needed This makes the production of the raw material rather ineffective and the availability of specific alloy powders difficult and expensive. The generated novel knowledge in MIM processing of these new systems shall be translated into the binder-based 3D printing technology. This novel technique did not require any mould. MIM of novel MgCa-alloy systems was carried out obtaining both sufficient material properties and biodegradation performance

Methods

Results

Conclusion