U.P.B. Sci. Bull., Series , Vol. , Iss. , 20 1 ISSN 1223 -7027 [623830]

U.P.B. Sci. Bull., Series …, Vol. …, Iss. …, 20 1 ISSN 1223 -7027
EXPERIMENTAL RESEARC H PROGRAM REGARDING THE
INFLUENCE OF THERMO -TIME TREATMENT OF
MULTI COMPONENT NI BASE MELTING ON THEIR
PROPERTIES IN SOLID PHASE
Valeriu RUCAI1, Nicolae CONSTANTIN 2, Cristian DOBRESCU3
Over the past decades has begun to increasingly pay attention to properties and structure of
metals and alloys in liquid phase , the motivation being both scientific ally and practical ly [1].
Particularly , especially in recent years, it has been demonstrated through the numerous studies,
that the structural characteristi cs of different metallic melting might heredity influence , sometimes
dramatically, the properties of the alloys after solidification.
That possibility constitutes, in fact, a treatment in liquid phase suggestively named Thermo -Time
Treatment .
In this respect, a complex experimental research program is proposed for a Ni-base alloy , used in
hot and high corrosive areas of aircraft engines .

Keywords : Thermo -Time Treatment (TTT), microstructure , Ni-alloy, aircraft
engines .
1. Introduction
Turbine industry for power plants but also the manufacture of Turbo -Jet
engine components from civil and military aeronautical industry have put the
issue of finding new materials to withstand both high temperature application and
environmental factors intensely corrosive [3],[5].
Researc h in this area have been channeled primarily upon the following two
categories of materials:
-Super alloys – refractories and corrosive resistant based on transition metals .
-Materials with very high refractivity : have been taken as a base material with
a very high melting point, such as chromium, refractory metals (Mo, W, etc.), but
also some ceramic materials.

1 Ph.D, Dept. of Engineering and Management for Obtaining of Metallic Materials, University
POLITEHNICA of Bucharest, ROMANIA , e-mail: [anonimizat]
2 Ph.D, Dept. of Engineering and Management for Obtaining of Metallic Materials, University
POLITEHNICA of Bucharest, ROMANIA , e-mail: [anonimizat]
3 Ph.D , Dept. of Engineering and Management for Elaboration of Metallic Materials, University
POLITEHNICA of Buch arest, ROMANIA, e -mail: [anonimizat]
4

Valeriu Rucai, Nicolae Constantin ,Cristian Dobrescu

Internationally, consistent efforts and investment research focused mainly on
the material in the first category, i.e. super alloys – refractories and corrosive
resistant based on transition metals. The main transition metals basically used in
the chemical composition of these super alloys are as following, in order of
importance: nickel, cobalt and iron.
Complex research es of thermochemical and thermomechanical processes
undergone by such a super alloy , on the one hand, research es in powder
metallurgy, on the other hand, have revealed a possible doubling of components
load resistance of Turbo -jets engines under temperatures of between 460 and 760o
C. These substantial improvement is a consequence of an increase in the index of
super plasticity , but most of all the resulted super fine crystalline grain with the
high level of isotropic characteristics.

2.Experimental

2.1..Class -Base Super alloys ,
Material chosen for the experiments is classified as super alloy -based nickel, used
in the aviation industry in hot and high corrosive areas of aircraft engines, more
precisely in the composition of jets and engines , operating at high levels of:
– Temperature : over 540oC (given to the region of mechanized guiding holes of
the turbine to the temperature up to 1100oC)
– Pressure ; -longitudinal elongation: effort between 10,000 -70,000 psi;
– Duration between two successive revisions: 12,000 hours.
Super alloy used in the experimental programs proposed: MSRR 7045
(Materials Super alloys Rolls -Royce 7045).
The main brands of super alloys that are part of this class and in a uniform
manner, as casting alloys (intended for precision molding ), are played according
to the table 1 :
Table 1
Class -Ni Base Super alloys

Mark Chemical Composition French
Standard
C
Si Mn Cr Mo W Al Co Ti Fe B Others Ni
MSRR
7045
≤0,1

≤0,6
≤0,6 20-
23 9-
10,5
≤0,6 0.7-
0.9 ≤1 2,4-
2,8
≤0,5
Ag ,B i,Pb
=0,0016 b P.E.R.
C 130
MSRR
7040
0,06

≤0,3
≤0,2
20

5,80
0.5
20
2,20
≤0,5 50
ppm Zr ≤ 200
ppm b P.E.R.
263 F
MSRR
7047
0,15

≤0,2
≤0,2
15,5

8,5
4,1
10
3,5
≤0,5 60
ppm b P.E.R.
C 1023

Experimental research program regarding the influence of Thermo -Time Treatment of
multi component Ni base melting on their properties in solid phase

2.2. Microstructure :
-austenite FCC – face-centred cube space lattice ( phase γ, matrix alloy):
Continuosly appearance of it represents a n FCC austenite phase in nickel
base, which usually contains a high percentage of solid solutions of some
components, such as Co, Cr, Mo, W, Ti, Al or Fe .
These components differs from the nickel with 1- 13% in atomic diameter.
Because pure nickel is not endowed with a high elasticity module or d iffusion
(two factors characterizing creep phenomena and tearing), matrix γ contributes to
the reliability of metal material in the most severe environmental conditions and
thus: superaliajele -based Ni can be used at temperatures in the range 0 .8Tmel and
endurance times of about 100,000 hours at the usual operating temperature .
– γ ' phase : phase precipitating major type (Ni, Co) 3 (Al, Ti). that can
appear as a phase of grain boundary: Al and Ti are added to the amounts
calculated separately superalloys or to substitute for each other in order to
precipitate fractions important dosing phase γ ' crystallized all the CFC system,
precipitation that is occurring in a manner coherent with austenite in the array.
-Carbonates : primary or secondary type MC: M23C6, M 7C3 (Cr 7C3, mainly)
and the M 6C that inhabits the grain boundaries (M -metal).
Carbonates appear to prefer submission to grain in Ni -based super alloy , this
being beneficial in terms of breaking resistance at elevated temperatures,
according to majority of researchers in the field.
-Intermetallic compounds geometrical (TCP , typologically close packed):
they may be Laves phases, or phases (vacancies compounds) μ or σ which causes
a sharp decrease for breaking strength and ductility.
All of these particularly complex phases are characterized by instability in the
structural and thermodynamic sense: according to their genesis the individual
phase s within the super alloys microstructure are not in equilibrium, but they tend
to evolve tow ard equilibrium with increasing temperature.
Many of these phases may change, depending on temperature and time –
keeping at that temperature. This may constitute a prerequisite for the design
study of a thermal time treatment (TTT), in the liquid phase, as the only
possibility of heat “correction” intervention , taking into account the nature of the
studied super alloy .

2.3. Stability of the Super alloy Surface
Properties involved here take into account the aggressiveness of the working
environment of these components made from super alloys:
Oxidation : in manufacturing industry of Turbo jets the oxidation is defined
as a super alloy reaction with oxygen in the presence of intermediate products

Valeriu Rucai, Nicolae Constantin ,Cristian Dobrescu

resulting from the combustion of “clean” fuels , i.e. without contamination, such as
Na, S and V.
A good oxidation resistance is obtained by forming a continuous thin films
and which acts as a diffusion barrier and is not exfoliating during thermal cycle
required by the operating environment of the engine.
Recently, the idea of small quantities of modifier has been taken into account:
very small amounts of yttrium , lanthanum and cerium, led to the removal of burns
and impr oved resistance to oxidation for many Ni and Co -based alloys or
refractory steels (austenitic Fe -base alloys).
Corrosion at high temperatures (sulphati ng): refers to a particular
aggressive attack result ed from a combined effect of usual oxidation process and
the sulfur and other contaminants reactions which are contained in combustion air
and/or proper fuel.
The main composed as “guilty " of warm corrosion seems to be sodium
sulphate, Na 2SO 4, which would finally dissolve protective oxide layer , making
place for sulfur diffusion by this layer inside metal matrix.
Sulphating is generally correlated with the content of chromium from super
alloy and with structural properties related to presence of sulphates.
Volatilization of Na2SO4 above 980oC makes sulphati ng at these
temperatures to be replaced by oxidation only while at temperatures below 980oC
the effect of corrosion at high temperatures can become dominant with on the
super alloy quality , consequently.

3. Integrated experimental program :

Starting from both micro unhomogeneousness and structural unequilibrium of the
multicomponent melting, generally speaking, and continuing with the
interconnection : metallurgical heredity – sensitive structural properties of melting
versus -properties in soli d phase the following experimental program has been
proposed for the Ni -base MSSR 7045 super alloy as described in the figure 1 ,
where:
VIF = Vacuum Induction (Melting) Furnace
pM = samples for primary working
pj = experimental melting samples
Tcr (σ) = critical temperature for TTT
TTT = Thermo -Time Treatment
Rm = Tensile Strength
Rp0.2 = Proof Stress as the amount of stress that will result in a plastic strain of
0.2%.

Experimental research program regarding the influence of Thermo -Time Treatment of
multi component Ni base melting on their properties in solid phase

EXPERIMENTS – MELTING
PHASE Samples -Melt
pM

LABORATORY
Graphite Resistance
Furnace
PILOT STATION
VIF IS-1 Leybold –
Heraeus (10kg)
Tcr (σ) –
after TTT

Tcr (σ) TTT
By undercooling TTT
No undercooling

TTT Samples, pj
ANALYSIS – SOLID SAMPLES
Macro structural
Analysis Microstructural
Analysis Wide Angle X –
Rays
Diffraction Stress Tests

CONCLUSIONS
Fig. 1. Integrated experimental program
Quantitativ e Qualitative Rm, R p0,2
HB Primary Working – MSRR 7045 : VIF Consarc (2 ,500 kg)
Sample Tcr

Valeriu Rucai, Nicolae Constantin ,Cristian Dobrescu

3. Conclusions
It can be said that the selection of a nickel base super alloy experimental
programme in order to research some variations of Thermo -Time Treatment had
the following main reasons:
1. Possible even duplication of tensile strength by obtaining small and
uniform grain size with a high i sotrop y of their properties;
2. Idea of substituting a possible modification process of the super alloy
structure by using heavy fusible particles (Titanium carbo -nitrides ) or lanthanides
in the aim of homogenization ;
3. Idea to "exploit" the phase instability, shown above, from the following
two points of view:
-improving the heredity of the solid product , therefore the possibility of a
state as close as possible of the structural equilibrium or even a
micro homogenization in its liquid state precisly because of the instability of these
phases.
It might be possible a smaller variety of close together orders resulting in
optimized solid state, consequently.
The resulted solid metallic material could present a composition with a n
acceptable quantity of intermetallic phases , carbide s with a certain size and shape
supported qualitatively by the u ser at the end of the day ;
– no heat treatment commonly used in the case of foundry alloys.

R E F E R E N C E S
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Mechanical Propertie of Superalloys – Base Ni , PhD Thesis , 1999 .
[2].I. Dragomir, V. Rucai, Studiul metodelor de îmbunătățire a performanțelor aliajelor pe
calea dirijării structurii în fază lichidă –Raport de cercetare nepublicat la Contract de
cercetare nr, 621/1996 MCT -UPB , faza 2/1998 .
[3]. A. K. Tihonov , The Influence of Heredity in the Elaboration of Steel and Pig Iron
Upon their Technological Properties , VI -th Conference Communication on issue “
Metallurgical Genetic Engineering ”, Samara , Russian Federation, 1998),
[4]. G. H. Geiger, D. R. Poirier, Transport Phenomena in Materials Processing , T.M.S. ,
USA , 1994.
[5]. A. Nohovoskii , Heredity in Metal Meltings, Theses of Scientific Conference,
Kuibishev, USSR, 1990) ,
[6]. B. A. Baum , Metal Meltings , Editura Tehnică, București, 1982.
[7]. *** – Interconnect ion between the Liquid and Solid States in Metals – Symposia,
Soci, Russian Federation, 1991.