Metallography basics: By which method is the micro-structure of a metallic specimen generally examined after proper surface preparation and etching?

Introduction / Context:
Metallography reveals grain size, phases, and defects that govern a metal’s properties. Routine quality control and failure analysis often begin with optical examination of polished and etched samples to interpret processing history and heat treatment response.

Given Data / Assumptions:

• Specimen has been mounted, ground, polished, and properly etched.
• Goal: typical, widely used method for micro-structural observation.
• We distinguish micro-structure imaging from crystallographic or bulk-NDT methods.

Concept / Approach:
An optical microscope (metallurgical microscope) provides magnifications up to roughly 1000× with reflected light, sufficient to resolve grains, pearlite lamellae spacing (coarsely), and distributions of phases/inclusions. X-ray techniques such as XRD identify crystal structure and texture but do not directly “image” micro-structures in real space at the scale needed for routine metallography. NDT methods like ultrasonics image internal flaws rather than surface micro-constituents. The naked eye cannot resolve true micro-structural features.

Step-by-Step Solution:
Define “micro-structure” as features resolvable at 50–1000×.Match method: optical microscopy with reflected illumination.Eliminate techniques aimed at crystallography (XRD) or bulk defects (UT).Choose “optical microscope”.

Verification / Alternative check:
Standard metallography texts begin with optical methods before advancing to SEM/TEM for finer scales.

Why Other Options Are Wrong:
Naked eye lacks required resolution.

X-ray techniques characterise phases and lattice parameters, not real-space micrographs at micrometre scale.

Ultrasonic testing is for internal defect detection and thickness gauging.

“None” is invalid because optical microscopy is correct and standard.

Common Pitfalls:
Assuming SEM is always required; in many cases, optical microscopy suffices and is more accessible.

Final Answer:
optical microscope