Lloyd A. Heldt
B.A., DePauw University; M.S. Indiana University
(physical chemistry), and Ph.D., University of
Pennsylvania (metallurgy)
Research Interests: Environmental effects on
mechanical properties, corrosion, machinability of
alloys.
Environmental effects on
mechanical properties
Our current studies are emphasizing the
environment-induced embrittlement of
intermetallic alloys. Several intermetallics are
extremely susceptible to embrittlement by water
vapor; among these are the iron aluminides,
alloys which otherwise have considerable
promise as structural materials because of their
low density, high resistance to corrosion and
oxidation, and low cost. It is suspected that for
these materials hydrogen embrittlement results
from the reaction of the alloy surface with water
vapor. Our work includes measurements of
fracture toughness and sub-critical crack growth
under controlled chemical and electrochemical
conditions to gain information about the kinetics
of embrittlement. Alloys for study are cast and
processed in our laboratories. Structural
characterization includes transmission electron
microscopy.
Free machining brass alloys
Tonnage quantities of leaded brasses are used in
manufacturing plumbing fittings and fixtures. The
lead, which appears as small inclusions in the
microstructure, promotes efficient and precise
machining. There is now evidence that the
minute quantities of lead dissolved from these
alloys by drinking water may have adverse health
effects and, for this reason, there is an urgent
need to develop free machining alloys that do not
contain lead. The means by which lead enhances
machinability is not well understood but it may
have simultaneous roles in lubrication and in local
embrittlement processes. Our work has as its
objective the characterization of the elemental
cutting and fracture processes. Based on the
findings of this work, experimental non-leaded
alloy compositions will be prepared and studied.
Aqueous corrosion of copper
Copper is generally extremely resistant to
corrosive attack by water. However, certain
municipal waters, obtained from wells, cause
pitting attack of copper water tube. The attack
involves the development of a local occluded
electrochemical cell, covered by a copper oxide
membrane, within which there is an enriched
chloride environment. As the demand for fresh
water continues to grow, there is an increasing
use of water from brackish wells and increasing
incidence of damage by this type of corrosion.
We intend to gain a better understanding of the
phenomenon through metallurgical and chemical
studies of the pitting attack and the dependence
of the attack on the water chemistry.