Conference, Proceedings

aerospace engineering, cryogenic engineering (liquefied natural gas tankers) etc. The third one
is alloy FeNi39 commonly used in thermostatic bimetals production (up to 400 0 C).
Temperature [ o C]
1000
800
600
400
200
α
α + γ (heating)
Tc = ~250 o C
Tc = ~195 o C
Tc = ~30 o C
α + γ (cooling)
Tc = ~560 o C
Tc = ~460 o C
0
-100
0 20 29 35 39 48 60 80 100
Nickel content wt. [%]
γ
magnetic
change
Figure 1:. Fe‐Ni Binary Alloy Phase Diagram with a prediction change of the Curie Point [2] as well as
with marked : compositions of FeNi48, and FeNi60 studied alloys; compositions of FeNi29, FeNi35
and FeNi39 invar alloys which have been investigated and described in [7]
This paper presents the results of the thermal diffusivity investigation of the two two‐
component FeNi48 and FeNi60 alloys at the identical temperature range (300 ÷ 900 K).
The first alloy is used in metal to glass seals, especially with soft glasses and for metal to
ceramic sealing applications (UV bulbs). The second alloy is applied in coated electrode
with a core wire of FeNi60, especially suited for welding of spheroidal cast iron. The
weld deposit is free from porosity and has the highest resistance to cracking.
2. Method of the measurement
The theoretical temperature distribution θ (x,t) = T(x,t) – T0 in the sample, where at time t = 0 the
surface layer (0< x ≤ g) absorbs radiation energy of the surface density Q , is obtained by solving
the Fourier equation, under the boundary conditions as it is shown in Figure 2. In this case the
general solution [5] is written as :
2
l
n
l
t nπx
nπx′
θ x t = x dx
e
x dx′
l ∫ θ ′ ′ + ∑ θ ′
l n l ∫
l
∞ −
1
2 τ
( , ) ( , 0)
cos ( , 0)
cos
0
= 1
0
(1)
2 2
where τ = l / π a ‐ is the characteristic time.
217