Export Datagridview to text file

Question

I have a small program that helps me to import excel sheets to a Datagridview to  later export it to a text file but the problem is that the text file is overwritten.  I would like  that every time you export the contents of datagridview a new file is created with a different name to avoid overwriting it . I would be very grateful for his help. I use the following code in a button to export the datagrid to text file:


If DataGridView1.RowCount = 0 Then
            MessageBox.Show("the datagridview is emptly")
        Else
            If Directory.Exists("C:\Foldertxt") = False Then 
                Directory.CreateDirectory("C:\Foldertxt")
            End If
            Dim sFile As String = "C:\Foldertxt\file.txt"
            If File.Exists(sFile) = True Then 
                My.Computer.FileSystem.DeleteFile(sFile, FileIO.UIOption.OnlyErrorDialogs, _
                                                  FileIO.RecycleOption.DeletePermanently, FileIO.UICancelOption.DoNothing)
            End If


           
   
            Using f As New IO.StreamWriter(sFile, True)

               
                Dim col As String = ""
               
                Dim row As String = ""
                Dim i As Integer = 0
                For Each r As DataGridViewRow In DataGridView1.Rows
                    For Each c As DataGridViewColumn In DataGridView1.Columns
                        row = row & "'" & Convert.ToString(r.Cells(c.HeaderText).Value) & "' "
                    Next
                    If i < DataGridView1.Rows.Count - 1 Then row &= Environment.NewLine
                Next

               
                f.WriteLine(row)
                MessageBox.Show("file created")
            End Using
        End IfI use Visual Studio 2013
Thank so much and sorry for my english