CAMT Material Properties & Characterization 2 — Questions and Answers
Question 1: Which characterization technique uses X-rays to determine the crystal structure and phase composition of a metal AM part?
- Scanning electron microscopy (SEM)
- X-ray diffraction (XRD) (Correct answer)
- Energy-dispersive X-ray spectroscopy (EDS)
- Optical profilometry
Correct answer: X-ray diffraction (XRD)
XRD identifies crystal phases by measuring diffraction angles caused by lattice spacing in the material's crystal structure.
Question 2: Residual stress in metal AM parts is primarily caused by:
- Slow cooling rates during build
- Rapid thermal cycling and non-uniform temperature gradients during solidification (Correct answer)
- Excessive powder layer thickness
- Low laser power settings
Correct answer: Rapid thermal cycling and non-uniform temperature gradients during solidification
The rapid heating and cooling cycles create steep thermal gradients that cause differential expansion/contraction, leaving residual stresses locked in the part.
Question 3: The tensile strength of a FDM part is generally highest when the applied load is oriented:
- Perpendicular to the build layers (Z-direction)
- Parallel to the build layers (XY-direction) (Correct answer)
- At a 45-degree angle to the build layers
- Direction has no effect on FDM parts
Correct answer: Parallel to the build layers (XY-direction)
FDM inter-layer bonds are the weakest link, so loads applied parallel to the layers avoid stressing those bonds, yielding higher strength.
Question 4: Which material characterization method uses a focused electron beam to image surface morphology at high magnification?
- Coordinate measuring machine (CMM)
- Scanning electron microscopy (SEM) (Correct answer)
- Differential scanning calorimetry (DSC)
- Computed tomography (CT) scanning
Correct answer: Scanning electron microscopy (SEM)
SEM uses a focused electron beam to produce high-resolution images of surface topography and microstructure.
Question 5: Differential Scanning Calorimetry (DSC) is used in AM material characterization to measure:
- Surface roughness of the part
- Thermal transitions such as melting point, crystallization, and Tg (Correct answer)
- Dimensional accuracy of the printed part
- Electrical resistance of the material
Correct answer: Thermal transitions such as melting point, crystallization, and Tg
DSC measures heat flow into or out of a material as a function of temperature, identifying phase transitions like melting, crystallization, and glass transition.
Question 6: Titanium alloys are widely used in metal AM for aerospace applications primarily because of their:
- Low melting point and ease of processing
- High strength-to-weight ratio and excellent corrosion resistance (Correct answer)
- Low cost compared to steel
- High electrical conductivity
Correct answer: High strength-to-weight ratio and excellent corrosion resistance
Titanium alloys offer exceptional strength relative to their density along with corrosion resistance, making them ideal for lightweight aerospace structures.
Question 7: In SLS (selective laser sintering) of nylons, the 'refresh rate' of powder refers to:
- How often the laser is recalibrated
- The ratio of new powder mixed with recycled powder to maintain consistent material properties (Correct answer)
- The speed at which new layers are deposited
- The frequency of bed temperature measurements
Correct answer: The ratio of new powder mixed with recycled powder to maintain consistent material properties
Recycled powder degrades with repeated thermal cycling, so blending it with fresh powder at a controlled ratio maintains consistent flowability and mechanical properties.
CAMT Material Properties & Characterization 2
Which characterization technique uses X-rays to determine the crystal structure and phase composition of a metal AM part?