Metallographic Preparation of Orthopedic Medical Devices

Abstract

Metallographic sample preparation methods for porous coated implant devices can be difficult due to inadequate fill of the mounting materials into the porous metallic structures. Inadequate fill of the mounting material during sample preparation leads to problems such as edge rounding, uneven etching, and metal smearing during polishing. These problems make proper microstructural identification and analysis difficult and/or inaccuate.

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Metallographic Preparation of Medical Devices

Specimen Mounting Program

Implant Specimens

  • Acetabular cup: Ti-6Al-4V substrate, CP Ti wire
  • Acetabular Cup: Ti-6Al-4V substrate, CP Ti Powder, Ta Beads
  • Femoral Hip Stem: Co-Cr-Mo with Co-Cr-Mo Beads
  • Femoral Knee: Co-Cr-Mo with Co-Cr-Mo Wire

Mounting Procedures

  • PhenoCure™thermosetting phenolic resin
  • Electroless Ni-plate/EpoMet® thermosetting resin
  • Vacuum impregnate with low-viscosity EpoThin® epoxy resin
  • Vacuum impregnate with EpoHeat™epoxy resin
  • SamplKwick® cast acrylic resin

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Low-Load Vickers Microindentation Hardness Testing

In 1925 in the UK, Smith and Sandland developed an indentation test that used a squarebased pyramidal-shaped indenter made of diamond[1]. The test was developed because the Brinell test (introduced in 1900), which (until recently) used a round hardened steel ball indenter, could not test steels harder than ~450 HB (~48 HRC). They chose this shape with an angle of 136° between opposite faces to obtain hardness numbers that would be as close as possible to Brinell hardness numbers for the same specimens over the usable Brinell range. This made the Vickers test easy to adopt, and it rapidly gained acceptance. The Vickers test has the great advantage of one hardness scale being used to test all materials, unlike the 30 different Rockwell test scales, each yielding numbers between ~20 and ~100.

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Light Microscopy

Nature of Light in Microscopy

Amplitude – light intensity
Wavelength – color;
Phase displacement;
Polarization – one plane of vibration

Laws of Refraction and Reflection

Part of the incident light ray is reflected and part is
refracted; the angle of reflection equals the angle of
incidence, i.e., θ = Φ

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Introduction to Metallography

What is Metallography

Metallography is the study of microstructure, how it is produced by composition and processing control, and the relationship between microstructure, mechanical and physical properties, and performance or service behavior. To examine the microstructure, we must prepare specimens properly so that the true structure, free of artifacts due to preparation, can be observed and properly identified, measured and interpreted.

What is Microstructure

Microstructure is the structure of a suitably prepare specimen as revealed by a microscope Microstructure consists of phases and/or constituents.
A phase is a physically homogeneous, mechanically separable portion of a material system. A constituent is a phase or combination of phases, which occurs in a characteristic configuration in an alloy microstructure.

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List of Articles

The articles and presentations that can be down-loaded from this web site are based upon work done by GFV while employed at Bethlehem Steel (1967-1983), Carpenter Technology (1983-1996), Buehler Ltd. (1996-2009) and Struers (2009-Present) and from the authors consulting work for companies such as, Latrobe Steel, Scot Forge, etc., and from his litigation work.

GFV's bylined articles appearing in various issues of the ASM Handbook series have been listed here courtesy of ASM International, Materials Park, Ohio.

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Influence of Specimen Preparation on SEM Images and Comparison to LOM Images

Influence of Specimen Preparation on SEM Images and Comparison to LOM Images

SEM and LOM are sometimes viewed as competitive methods; but, they are actually complementary. Some people believe that specimen preparation is less critical for SEM work than for LOM work; but, the reverse is true. Image forming mechanisms for the LOM and the SEM are different – we should make the most of these differences. The LOM is a more efficient tool for fast, low magnification (≤ 2000X) examination of a specimen – use it first to determine if, and where, one should follow with higher magnification SEM examination and EDS or EBSD work.

Prepare every specimen for SEM examination with the quality required for EBSD work; this is actually quite easy with the right equipment, consumables and methods. Examples of preparation methods for many metals/alloys and other materials can be found in Struers publications and web site. Examples of LOM and SEM images of specimens that were properly prepared or poorly prepared will be shown.

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Last Updated on Wednesday, 06 February 2013 18:15

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resourcesThe articles and presentations that can be down-loaded from this web site are based upon work done by GFV while employed at Bethlehem Steel (1967-1983), Carpenter Technology (1983-1996), Buehler Ltd. (1996-2009) and Struers (2009-Present) and from the authors consulting work for companies such as, Latrobe Steel, Scot Forge, etc., and from his litigation work. GFV's bylined articles appearing in various issues of the ASM Handbook series have been listed here courtesy of ASM International, Materials Park, Ohio.

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