Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2000-07-31
2003-07-08
Kwok, Helen (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S609000, C073S620000, C073S629000
Reexamination Certificate
active
06588278
ABSTRACT:
BACKGROUND OF THE INVENTION
1. a) Field of the Invention
This invention relates to an ultrasonic inspection device useful for the nondestructive inspection of a metallic material, for example, an ultrasonic inspection device suitable especially for the evaluation of soundness of a surface layer of a specimen. In addition, the present invention is also concerned with an ultrasonic probe useful for the nondestructive inspection of a specimen, especially with an ultrasonic probe suitable for the evaluation of soundness of a surface layer of a specimen and also for the detection of directionality of a flaw occurred in a specimen.
2. b) Description of the Related Art
As is described, for example, in JP 4-238265, it is conventionally known to nondestructively evaluate the adhesion of a spray deposit, which is formed on a surface of a metallic material, by using an ultrasonic wave.
To evaluate the adhesion of two materials at their interface, it has been a common practice to arrange a focused ultrasonic probe in opposition to the specimen, to bring the focal point of a supersonic wave, which has been transmitted from the ultrasonic probe, into registration with the interface between the two materials and then to detect the intensity of an echo from the interface. When the specimen is a spray deposit formed on a surface of a base material, however, the spray deposit is a thin film of 0.1 to 0.3 mm or so. Transmission of an ultrasonic wave to the specimen from the side of the spray deposit, therefore, practically does not make it possible to separate an echo from a surface of the spray deposit and an echo from an interface from each other, thereby failing to evaluate the adhesion of the spray deposit to the base material. Discussing, for example, about a 0.1-mm thick WC-based spray deposit formed on a surface of a base material, it is only an ultrasonic wave the frequency of which is within a range of from 5 to 20 MHz (200 to 50 ns in terms of period) that can be used for inspection because the spray melt causes a considerable high-frequency attenuation and has irregularities of from several micrometers to several tens micrometers or so on its surface. On the other hand, as the speed of a longitudinal wave through the spray deposit is about 4,200 m/s and the time difference between an echo from the surface of the spray deposit and an echo from the interface is only as small as 47.6 ns, it is understood that these echoes cannot be separated from each other.
Reference is now had to FIG.
1
. In the spray deposit evaluation method described in the above-described conventional art, a specimen S with a spray deposit S
2
formed on a surface of a base material S
1
and a focused ultrasonic probe
101
are arranged in a face-to-face relationship in water (in the drawing, sign W indicates water as a medium for an ultrasonic wave) , and a focal point of the ultrasonic probe
101
is brought into registration with a bottom surface of the base material S
1
. From the intensity of a bottom echo, the adhesion of spray deposit S
2
to the base material S
1
is determined. According to this method, poor adhesion at the interface leads to more reflection of the ultrasonic wave at the interface, resulting in a decrease in the intensity of an echo from the bottom surface of the base material, while good adhesion at the interface allows an ultrasonic wave to transmit well through the base material S
1
, resulting in an increase in the intensity of an echo from the bottom surface of the base material. Therefore, the adhesion of the base material and the spray deposit at their interface can be determined. It is also possible to ascertain an adhesion distribution of the spray deposit S
2
by two-dimensionally scanning a surface of the specimen S with the ultrasonic probe
101
, inputting bottom echo levels at appropriate pitches and then displaying said bottom echo levels as an image on a C-scope.
According to the melt deposit evaluation method disclosed in the above-described conventional art, however, the ultrasonic wave
201
is transmitted to the specimen S from the side of the spray deposit S
2
, and bottom echo levels of the base material S
1
are detected. Therefore, as is depicted in FIG.
2
A, the irradiation diameter d of the ultrasonic beam on the surface of the spray deposit S
2
becomes greater and the detecting ability of a flaw drops, as the thickness h of the base material S
1
becomes greater.
For similar reasons as described above, the spray deposit evaluation method disclosed in the above-described conventional art leads to occurrence of a flaw inspection infeasible region at a relatively large region where, as shown in
FIG. 2B
, an end portion e of the specimen
100
is outside an irradiation range of the ultrasonic beam when two-dimensional scanning is performed along the surface of the specimen S by the ultrasonic probe
101
. The end portion e of the specimen S is a location where a flaw tends to occur in the spray deposit S
2
, and is especially important as a location to be inspected. Inclusion of such a large flaw inspection infeasible region is of a serious concern from the standpoint of increasing the reliability of a flaw inspection.
Further, the spray deposit evaluation method disclosed in the above-described conventional art is a method in which the adhesion between the base material S
1
and the spray deposit S
2
is indirectly evaluated from the levels of bottom echoes from the base material S
1
. In addition to information indicative of the adhesion of the spray deposit S
2
, the bottom echoes from the base material S
1
, however, contain various information indicative of internal and bottom conditions of the base material S
1
, for example, information on irregularities of the bottom surface and rust and the like deposited on the bottom surface and information on flaws inside the base material. Because these information and the information on the adhesion of the spray deposit S
2
cannot be separated from each other, the conventional spray deposit evaluation method is accompanied by a problem in that the evaluation of the spray deposit cannot be conducted precisely.
Moreover, for similar reasons as described above, the spray deposit evaluation method disclosed in the conventional art cannot obtain sufficient or complete bottom echoes and hence, cannot perform a practically sufficient inspection for a flow inside a spray deposit, when the base material S
1
comprises a material through which an ultrasonic wave undergoes a significant attenuation like nickel-based super alloys.
A description has been made above by taking, as an example, an inspection of a flaw in a spray deposit. It is however to be noted that similar inconveniences arise upon evaluating the soundness of a surface layer of a specimen in other characteristics and the like, such as existence
on-existence of a crack in the surface layer of the specimen, a stress distribution in the surface layer of the specimen, a fracture toughness value, thermal embrittlement or intergranular corrosion.
As is disclosed, for example, in JP 10-318995, a further technique is also known to nondestructively evaluate a stress distribution and a fracture toughness value of a specimen and also a deterioration of the specimen such as thermal embrittlement and intergranular corrosion (these properties will hereinafter be collectively called “deterioration or the like of a specimen”) from variations in the speed of a leaked elastic surface wave which is one of ultrasonic modes.
FIG.
3
A and
FIG. 3B
are a fragmentary cross-sectional view and a plan view, which illustrate one example of ultrasonic probes which have been conventionally used in this type of nondestructive inspections. As is readily appreciated from these drawings, an ultrasonic probe
101
has a construction that it is provided with a single-piece oscillator
102
formed in a disc shape in plan and an acoustic lens
103
in the form of a concave lens, said acoustic lens being for causing an ultrasonic wave, which has been transmitted from the oscillator
102
, to conv
Takishita Yoshihiko
Yamamoto Hiroshi
Crowell & Moring LLP
Hitachi Construction Machinery Co. Ltd.
Kwok Helen
Saint-Surin Jacques
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