Microstructure and Deformation Response of TRIP-Steel Syntactic Foams to Quasi-Static and Dynamic Compressive Loads.

David Ehinger,Lutz Krüger,Ulrich Martin,Alexander Funk,Joachim Baumeister,Anja Waske,Jörg Weise

doi:10.3390/ma11050656

Abstract

The implementation of hollow S60HS glass microspheres and Fillite 106 cenospheres in a martensitically transformable AISI 304L stainless steel matrix was realized by means of metal injection molding of feedstock with varying fractions of the filler material. The so-called TRIP-steel syntactic foams were studied with respect to their behavior under quasi-static compression and dynamic impact loading. The interplay between matrix material behavior and foam structure was discussed in relation to the findings of micro-structural investigations, electron back scatter diffraction EBSD phase analyses and magnetic measurements. During processing, the cenospheres remained relatively stable retaining their shape while the glass microspheres underwent disintegration associated with the formation of pre-cracked irregular inclusions. Consequently, the AISI 304L/Fillite 106 syntactic foams exhibited a higher compression stress level and energy absorption capability as compared to the S60HS-containing variants. The -martensite kinetic of the steel matrix was significantly influenced by material composition, strain rate and arising deformation temperature. The highest ferromagnetic -martensite phase fraction was detected for the AISI 304L/S60HS batches and the lowest for the TRIP-steel bulk material. Quasi-adiabatic sample heating, a gradual decrease in strain rate and an enhanced degree of damage controlled the mechanical deformation response of the studied syntactic foams under dynamic impact loading.

Highlights

Syntactic foams form a subgroup of cellular solids and consist of hollow glass, carbon or ceramic microspheres acting as porosity-producing agents and simultaneously as stiff reinforcements homogeneously distributed in a continuous matrix, as well-known from particulate composites [1,2,3]
The present study dealt with the investigation of AISI 304L TRansformation Induced Plasticity (TRIP)-steel syntactic foams containing soda-lime borosilicate glass microspheres or alumino-silicate cenospheres and focuses on their role on the crush resistance and microstructural characteristics of the foam
While the Fillite 106 cenospheres retain their initial shape, the S60HS glass microspheres undergo disintegration during processing accompanied with the formation of pre-cracked irregular glass inclusions and occurring chemical reactions with the surrounding steel matrix

Summary

Introduction

Syntactic foams form a subgroup of cellular solids and consist of hollow glass, carbon or ceramic microspheres (microballoons) acting as porosity-producing agents and simultaneously as stiff reinforcements homogeneously distributed in a continuous matrix, as well-known from particulate composites [1,2,3]. Materials 2018, 11, 656 processing including pressure infiltration, die casting, stir casting ( in combination with hot extrusion), gravity-fed infiltration, and powder metallurgy routes (e.g., metal powder injection molding (MIM)) [6,7]. The latter is very beneficial since the range of microsphere volume fractions can be widely varied and matrix compositions, which are not suited for liquid metal processing, as well as high-melting matrices can be used [3]. Glass microspheres of type iM30K or S60HS (soda-lime borosilicate glass), alumina spheres and cenospheres (fly ash from coal combustion process) were typically used as secondary components [5,15,16,17,18,19]

Objectives

Methods

Results

Discussion

Conclusion