Page 20 - Demo

Issue 143 August 2024 PCMI Journal 20
PCM of Difficult-to-Etch Metals and Alloys: Nickel- and Cobalt-Based Superalloys
Emeritus Professor David Allen, Cranfield University
Allen et al reported the PCM of Ni-Span-C Alloy 902 (UNS N09902) - an extremely
strong, precipitation-hardenable iron-nickel superalloy (42.5% Ni, 49% Fe%,
5.3% Cr, 2.4% Ti) with a thermoelastic coefficient that can be controlled by the
amount of cold work and heat treatment temperature. The product, a small
transducer body for in vivo blood pressure measurement (100 μm thick and
approx.2.3 x 0.7 mm), sits within a vein or artery and is placed in situ by means
of a hypodermic syringe. It was etched successfully, using a two-stage process,
in 3.4M (42°Bé) ferric chloride solution at 30°C [10].
This paper concentrates on the capability of PCM to produce etched parts from
a wide range of nickel- and cobalt-based superalloys, a topic never previously
discussed at a PCMI Conference.
Useful information on PCM of various Inconel alloys has been found in some
recent research publications from India [11-13].
An Internet and e-mail review of the capability of PCM companies to etch various
Inconel alloys, classified by geographical location, is shown in Table 4. If a
company has the capability of etching thin material only, the capability was
reduced to 0.5*
.
Table 4. PCM company capabilities to etch various Inconel alloys.
PCM companies and their locations Inconel alloys
600 601 617 625 718 X-750
USA (9)9)(9) 6 3 1 1.5* 2 6
UK and Europe (8) 5 3 3 1 1 2
Total (17) 11 6 4 2.5 3 8
Company capability to etch specific Inconel alloys 65% 35% 24% 15% 18% 47%
The compositions of some Inconel alloys that affect their etchability are shown
in Table 5. The easiest elements to etch are highlighted in green, more difficult
to etch in yellow and the most difficult to etch in red.
It is therefore anticipated that Inconels 600, 601 and X-750 will be the easiest
materials to etch followed by Inconels 617 and 718 with Inconel 625 being the
most difficult material to etch. This appears to be borne out in practice as
appeals to PCM companies for examples of etched Inconel parts produced three
components etched from Inconel X-750, two from Inconel 600 and one from
Inconel 718.
Table 6 shows the results published on the etching of Inconels in ferric chloride.