Prakt. Met. Sonderband 38 (2006) 81
ston MICROSTRUCTURE CHARACTERIZATION OF MOLYBDENUM
By ALLOYS AFTER HOT DEFORMATION
e des : .
ede der T. Mrotzek, Ch. Wüstefeld, A. Hoffmann*, U. Martin
2samten | = . | | .
Istandig Institut fur Werkstoffwissenschaft, TU Bergakademie Freiberg, Freiberg, Germany
bar. PLANSEE Metall GmbH, Reutte, Austria
ABSTRACT
The high temperature deformation of powder metallurgical produced Mo-based alloys was
investigated by hot rolling, tensile and creep tests. The present study examines the effect
of thermomechanical treatments on the microstructure evolution of Molybdenum-Titanium
and TZM (Titanium-Zirconium-Molybdenum). The microstructure characterization was
carried out by optical and scanning electron microscopy (SEM), electron backscattering
diffraction (EBSD) and transmission electron microscopy (TEM).
It has been appointed that the two investigated molybdenum alloys tend to form a distinct
} dislocation substructure with subgrains. Using a particular thermomechanical treatment
ent one is also able to produce an ultrafine subgrain by isothermal hot rolling. The estimated
Abbil- microstructural parameters like dislocation density, subgrain size and Taylor factors
affecting the yield stress and recrystallization behaviour of the molybdenum alloy TZM.
Subgrain hardening was considered to be the dominant hardening mechanism after hot
deformation. TZM creep behaviour is characterized by creep via dislocation mechanisms.
The measured subgrain size refinement correlates quite well with the pronounced primary
creep of TZM crept at 1200°C.
nie zur
dungen
optische
1. INTRODUCTION
ı auch
wohl an Due to their high melting point, molyodenum and its alloys are often manufactured by
deutlich powder-metallurgy. The as sintered material exhibits mechanical properties which are not
ethoden well suited for most applications. Thus the desired strength and ductility has to be set by
e kurze several thermomechanical treatments after sintering. Higher degrees of deformation can
polieren not be achieved without annealing. Occurrence of recrystallization is connected to a
hischen decrease in strength. Therefore recrystallization limits the working temperature but
materials deform more easily during processing. In the past few decades the demand for
sffenden high temperature materials increases and there is a demand for higher service
temperatures at the same time. The use of molybdenum and its alloys as high temperature
materials is based on their high strength and strong creep resistance at hot conditions.
The development of these alloys was mainly driven by the interest of special industries like
| . aircraft and space, nuclear and lightening. For lightening applications these materials are
ange in used as wires with a typical range of 0.1 —1.0 mm or as foil material with thicknesses down
Aarx- to 0.03 mm. TZM has been a well accepted molybdenum alloy for high temperature
applications since the late 60’s.
ktrolyti- Comparing the solid solution alloy Mo-0.5wt.-%Ti with the alloy TZM (Mo-0.5Ti-0.08Zr-
INSECT 0.01-0.04C), the strength level of the particle containing material is superior to that of Mo-
Ti solid solution alloy. TZM is considered as particle strengthened material. The intention is
