Process for reconstituting the grain structure of metal surfaces

Claim 2

A process for treating a refractory metal surface of a metal object to make the surface more ductile and to thereby enhance resistance of the surface to brittle fracture, comprising: a. establishing the object surface at a temperature at least above its nil ductility temperature, b. applying an intense electron beam repetitively to a surface of the object to heat the surface transiently at least 350 times at a high rate and simultaneously restricting the time of each beam application below the time during which substantial grain growth would occur while maintaining the object surface at a temperature near but below its melting temperature and at least above its nil ductility temperature, thereby creating repetitive high temperature gradients and resultant stresses in the surface layer which reconstitute the grain structure thereof, and c. continuing said repetitive application of said electron beam until said surface layer has a substantially continuous polygonized subgrain structure which is finer than the grain structure of the metal below the surface layer.

Claim 3

A process for treating a surface of a refractory metal object to make the surface more ductile and thereby enhance resistance of at least a part of the surface to brittle fracture, comprising: a. directing onto the surface of an object an electron beam which has sufficient energy to slowly elevate at least the surface region which is to be treated to a temperature at least above its nil ductility temperature and then b. increasing the energy of the electron beam and concentrating it on a small area increment of the surface while maintaining relative motion between the beam and the surface, the increased beam energy being sufficient to both maintain the region being treated at a temperature at least above its nil ductility temperature and to heat the surface during intermittent short intervals at a high rate while the time-average temperature of the metal is maintained below a temperature at which grain growth may occur, and below but near the melting temperature of the surface, thereby creating repetitive high temperature gradients and resulting stresses in the surface layer which reconstitute the grain structure thereof, and c. continuing the application of said electron beam until said surface layer has a substantially continuous polygonized subgrain structure which is finer than the grain structure of the metal below the surface.

Claim 4

The process set forth in claim 3 wherein relative motion is obtained between the electron beam and the surface of the object by the steps of: a. moving the object in a direction extending through the beam path, and b. sweeping the beam at a relatively higher rate of movement along a straight line that is substantially normal to the line of movement of the object.

Claim 5

The process set forth in claim 3 wherein relative motion between the object and the electron beam is obtained by the steps of: a. directing the beam in a fixed path whereby it impinges on the surface of the object, and b. rotating the object.

Claim 6

The process set forth in claim 3 including the steps of: a. moving the object repetitively through the path of the electron beam, and b. pulsing the electron beam on and off sequentially with the on time, the off time, the energy density of the beam and the rate of object movement being so adjusted and related that there is development of optimum heat in the surface for creating the requisite high thermal gradients and stresses.

Claim 7

The process set forth in claim 3 including the steps of: a. moving the object along a line extending through the beam path, and b. sweeping the electron beam at a relatively higher rate of movement along lines that substantially parallel each other on the surface and are substantially normal to the line of movement of the object with the sweeping velocity of the beam, the energy density of the beam and the velocity of the object being so adjusted and related that there is development of optimum heat in the volume increments for creating the requisite high thermal gradients and stresses.

Claim 8

A process for treating a refractory metal target surface which is intended for production of X-rays in an X-ray tube for increased ductility in the surface so as to increase its resistance to brittle fracture, comprising the steps of: a. disposing the target in an evacuable enclosure and in the path of an electron beam that may be generated in the enclosure and directed onto the target surface, b. rotating the target, c. gradually preheating the target to a temperature at least above its nil ductility temperature by impingement thereon of an electron beam which is adjusted to a suitably low energy level, d. adjusting the accelerating voltage and current of the electron beam to a higher combination of values that results in introducIng enough heat in the surface to melt the metal but for the target being rotated, thereby producing repetitive high temperature gradients and stresses in the surface which reconstitutes the grain structure in a surface layer of the target, and e. continuing the application of said electron beam to said target surface until its surface layer has a substantially continuous polygonized subgrain structure which is finer than the grain structure of the metal below the surface.